History management program, history management method, and history management device

Abstract

To provide a history management program, a method for managing a history, and a history management device that can realize a function of cancelling the immediately preceding operation and recreating the original state.SOLUTION: A display device receives an input operation for updating the content of display of the display unit (S11:YES, S13:YES). The display device stores data code Cm showing the content of display updated according to the received input operation as data code Cm showing the latest display content (S19). The display device determines a UNDO code necessary to return the latest display content to pre-update display content as the display content before the update (S29). The display device stores, as history information, the determined UNDO code related to the sequence of operations as the sequence of the received input operations (S31).SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a history management program, a history management method, and a history management device. [Background technology]

[0002] There is known a device that stores an operation history in a storage unit when an operation is performed to input, change, delete, etc., characters or images. For example, in the input device described in Patent Document 1, stroke data of a character string input by handwriting operation is stored in a stroke data storage unit in the order of the operations.

[0003] A function that cancels the most recently performed operation and returns to the original state is generally known as an UNDO function. Here, as in Patent Document 1, an example is taken of a case where the UNDO function is implemented in a device that stores information indicating addition operations for adding new characters or images (hereinafter referred to as "addition operation information") in the order of operations as history information. In this case, the UNDO function can be implemented by referencing one piece of addition operation information from the stored history information in the reverse order of the operations, and canceling the addition operation indicated by the referenced addition operation information. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-265171 Summary of the Invention [Problem to be solved by the invention]

[0005] A modification operation that modifies input characters or images, or a deletion operation that deletes input characters or images, may be performed together with an addition operation. In this case, the history information includes not only addition operation information, but also modification operation information indicating the modification operation and deletion operation information indicating the deletion operation. In this case, when attempting to implement the UNDO function, it may not be possible to undo the most recently performed operation and return to the original state using only one piece of operation information referenced from the history information in the reverse order of the operations. As such, with history information that stores operation information in the order of operations, it may be necessary to reference multiple pieces of operation information to implement the UNDO function, which is inefficient.

[0006] An object of the present invention is to provide a history management program, a history management method, and a history management device that efficiently realize a function for canceling an immediately preceding operation and restoring the previous state. [Means for solving the problem]

[0007] A history management program according to a first aspect of the present invention is characterized in that it causes a computer to execute the following steps: a first reception step of receiving an input operation for updating the display content of a display unit; a first storage step of storing the display content updated in accordance with the input operation received in the first reception step in a storage unit as latest display content; a first determination step of determining an UNDO process required to restore the latest display content to the pre-update display content, which is the display content before the update; and a second storage step of associating the UNDO process determined in the first determination step with an operation sequence, which is the order of the input operations received in the first reception step, and storing the UNDO process in the storage unit as history information.

[0008] When a computer executing a history management program receives an instruction to execute an UNDO function that cancels the most recent operation and returns the display to the original state, the computer references the history information and executes the selected UNDO process in the reverse order of the operations, thereby realizing the UNDO function. Therefore, the computer can implement the UNDO function efficiently because it does not need to reference multiple pieces of information stored as history information.

[0009] A history management method according to a second aspect of the present invention includes a first receiving step of receiving an input operation for updating display content on a display unit, a first storing step of storing the display content updated in accordance with the input operation received in the first receiving step in a storage unit as latest display content, a first determining step of determining an UNDO process required to restore the latest display content to the pre-update display content that is the display content before the update, and a second storing step of associating the UNDO process determined in the first determining step with an operation order that is the order of the input operations received in the first receiving step, and storing the UNDO process in the storage unit as history information. According to the third aspect, it is possible to achieve the same effect as the first aspect.

[0010] A history management device according to a third aspect of the present invention comprises a display unit, a first receiving means for receiving an input operation for updating display content displayed on the display unit, a first storage means for storing the display content updated in accordance with the input operation received by the first receiving means in a storage unit as latest display content, a first determining means for determining an UNDO process required to restore the latest display content to the pre-update display content that is the display content before the update, and a second storage means for associating the UNDO process determined by the first determining means with an operation order that is the order of the input operations received by the first receiving means, and storing the UNDO process determined by the first determining means in the storage unit as history information. The fourth aspect can achieve the same effects as the first aspect and claim 1. [Brief explanation of the drawings]

[0011] [Figure 1]2 is a diagram showing an overview and an electrical configuration of a display device 3. FIG. [Figure 2] FIG. 10 is a diagram showing history information Ud stored in a conventional method. [Figure 3] FIG. 2 is a diagram showing history information Us stored in the present embodiment. [Figure 4] FIG. 10 is a diagram showing an example of a display screen 5A. [Figure 5] 10 is a flowchart showing a first flag control process. [Figure 6] 10 is a flowchart showing a first main process. [Figure 7] 7 is a flowchart showing the first main processing, which is a continuation of FIG. 6. [Figure 8] 8 is a flowchart showing the first main processing, which is a continuation of FIG. 7. [Figure 9] 1 is a diagram illustrating an overview of a communication system 1 and an electrical configuration of a server device 2. FIG. [Figure 10] FIG. 2 is a diagram showing a communication sequence in the communication system 1. [Figure 11] FIG. 10 is a diagram showing an example of a display screen 5B. [Figure 12] 10 is a flowchart showing a second flag control process. [Figure 13] 10 is a flowchart showing a second main process. [Figure 14] 14 is a flowchart showing the second main processing, which is a continuation of FIG. 13. [Figure 15] 15 is a flowchart showing the second main processing, which is a continuation of FIG. 14. [Figure 16] 16 is a flowchart showing the second main processing, which is a continuation of FIG. 15. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described with reference to the drawings. The drawings are used to explain technical features that can be adopted by the present invention, and the configurations of the devices described therein are merely illustrative examples and are not intended to limit the scope of the present invention.

[0013] First Embodiment <Configuration of display device 3> 1, an overview of the display device 3 will be described. The display device 3 is a well-known tablet terminal. The display device 3 has a CPU 31, a ROM 32A, a RAM 32B, a flash memory 32C, a display unit 33, an input unit 34, and a communication interface (I / F) 35.

[0014] The CPU 31 is responsible for overall control of the display device 3. The ROM 32A stores a boot program and initial setting information. The RAM 32B temporarily stores data while the CPU 31 is executing processing. The flash memory 32C stores a control program to be executed by the CPU 31, data codes Cm and Ch described below, history information Us, etc. The display unit 33 is a liquid crystal display. The input unit 34 is a touch panel provided on the surface of the display unit 33. The communication I / F 35 is a communication module for communicating with the server device 2 (see FIG. 9) via the network line 4 and access point 4A (see FIG. 9) described below.

[0015] <History Information Us> A case will be described in which an input operation for updating the display content displayed on the display unit 33 in the display device 3 is performed via the input unit 34. FIGS. 2 and 3 show the latest display content of the display unit 33 after each input operation, a data code Cm indicating the latest display content, and history information Ud (see FIG. 2) and Us (see FIG. 3). FIGS. 2 and 3 show a plurality of common input operations performed in sequence. The data code Cm is written in JSON format and is the same in FIGS. 2 and 3. The history information Ud and Us are different in FIGS. 2 and 3. FIG. 2 shows history information Ud stored using a conventional method for comparison. FIG. 3 shows history information Us stored using the method of this embodiment.

[0016] 2, first, an input operation is executed to add and display a new image (character string "Hi!") on the 0th line of the display unit 33. Hereinafter, the input operation to add and display a new image will be referred to as an "addition operation."

[0017] In this case, the command "add" indicating that a new image is to be added to the display unit 33 and displayed, the type "text" indicating that the image type is a character string, the line "0" indicating the position where the image is to be added, and the instruction code "add / text / 0 "Hi!"" including the character string "Hi!" to be added are executed. As a result, as shown in FIG. 2(B), "Hi!" is added to the 0th line of the data code Cm. Also, the character string "Hi!" is displayed on the 0th line of the display unit 33, and the display content is updated. Furthermore, the executed instruction code "add / text / 0 "Hi!"" is added to the history information Ud. The added instruction code "add / text / 0 "Hi!"" is associated with the operation order "001" indicating the order in which the input operation was accepted.

[0018] Next, an add operation is executed to add a new character string "Bye!" to the first line of the display unit 33. In this case, the instruction code "add / text / 1 "Bye!"" containing the command "add", type "text", line "1", and the image to be added "Bye!" is executed. As a result, "Bye!" is added to the first line of the data code Cm, as shown in FIG. 2(C). Also, the character string "Bye!" is added to the first line of the display unit 33, and the display content is updated. Furthermore, the executed instruction code "add / text / 1 "Bye!"" is newly added to the history information Ud. The added instruction code "add / text / 1 "Bye!"" is associated with the operation order "002".

[0019] Next, an input operation is executed to change the character string "Hi!" displayed on the 0th line of the display unit 33 to another character string "Hello!". Hereinafter, an input operation to change the image displayed on the display unit 33 to another image will be referred to as a "change operation."

[0020] In this case, the instruction code "replace / text / 0 "Hello!"" is executed, which includes the command "replace" indicating that the image is to be changed, the type "text," the line "0" indicating the line where the image is to be changed, and the changed string "Hello!". As a result, as shown in FIG. 2(D), the 0th line of the data code Cm is changed to "Hello!". Also, the string "Hi!" (see FIG. 2(C)) displayed on the 0th line of the display unit 33 is changed to the string "Hello!", and the display content is updated. Furthermore, the executed instruction code "replace / text / 0 "Hello!"" is newly added to the history information Ud. The added instruction code "replace / text / 0 "Hello!"" is associated with the operation order "003."

[0021] Next, an input operation is performed to delete the character string "Bye!" displayed on the first line of the display unit 33. Hereinafter, the input operation to delete the image displayed on the display unit 33 will be referred to as a "delete operation."

[0022] In this case, the instruction code "remove / text / 1" is executed, which includes the command "remove" indicating that the image is to be deleted, the type "text", and the line "1" from which the image is to be deleted. As a result, the first line of the data code Cm is deleted, as shown in FIG. 2(E). Also, the character string "Bye!" (see FIG. 2(D)) displayed on the first line of the display unit 33 is deleted, and the display content is updated. Furthermore, the executed instruction code "remove / text / 1" is newly added to the history information Ud. The added instruction code "remove / text / 1" is associated with the operation sequence "004".

[0023] On the other hand, in the second example shown in Fig. 3, the history information Us is stored in a different way from the first example shown in Fig. 2. The details are as follows.

[0024] First, an operation to add the character string "Hi!" to the 0th line of the display unit 33 is executed. In this case, the command code "add / text / 0 "Hi!"" (see FIG. 2(B)) is executed. As a result, as shown in FIG. 3(B), "Hi!" is added to the 0th line of the data code Cm. Furthermore, the character string "Hi!" is displayed on the 0th line of the display unit 33, and the display content is updated.

[0025] Furthermore, the command code required to restore the updated display content (see FIG. 3(B)) to the display content before the update (see FIG. 3(A)) is determined. Specifically, this is as follows. To restore the updated display content shown in FIG. 3(B) to the display information before the update shown in FIG. 3(A), the character string "Hi!" displayed on line 0 of the display unit 33 is deleted. For this reason, the command code "remove / text / 0" is determined, which includes the command "remove," the type "text," and the line "0." The determined command code is newly added to the history information Us. The added command code "remove / text / 0" is associated with the operation sequence "001."

[0026] Next, an operation to add the character string "Bye!" to the first line of the display unit 33 is executed. In this case, the command code "add / text / 1 "Bye!"" (see FIG. 2(C)) is executed. As a result, as shown in FIG. 3(C), "Bye!" is added to the first line of the data code Cm. In addition, the character string "Bye!" is displayed on the first line of the display unit 33, and the display content is updated.

[0027] Furthermore, the command code required to restore the updated display content (see FIG. 3(C)) to the display content before the update (see FIG. 3(B)) is determined. Specifically, this is as follows. To restore the updated display content shown in FIG. 3(C) to the display information before the update shown in FIG. 3(B), the character string "Bye!" displayed on the first line of the display unit 33 is deleted. Therefore, the command code "remove / text / 1" is determined, which includes the command "remove," the type "text," and the line "1." The determined command code is newly added to the history information Us. The added command code "remove / text / 1" is associated with the operation sequence "002."

[0028] Next, a change operation is executed to change the character string "Hi" displayed on line 0 of the display unit 33 to the character string "Hello!". In this case, the command code "replace / text / 0 "Hello!"" (see FIG. 2(D)) is executed. As a result, as shown in FIG. 3(D), line 0 of the data code Cm is changed to "Hello!". Also, the character string "Hi!" (see FIG. 3(C)) displayed on line 0 of the display unit 33 is changed to the character string "Hello!", and the display content is updated.

[0029] Furthermore, a command code required to restore the updated display content (see FIG. 3(D)) to the display content before the update (see FIG. 3(C)) is determined. Specifically, this is as follows. To restore the updated display content shown in FIG. 3(D) to the display information before the update shown in FIG. 3(C), the character string "Hello!" displayed on line 0 of the display unit 33 is changed to the character string "Hi!". Therefore, a command code "replace / text / 0 "Hi!"" containing the command "replace", type "text", line "0", and character string "Hi!" is determined. The determined command code is newly added to the history information Us. The added command code "replace / text / 0 "Hi!"" is associated with the operation sequence "003".

[0030] Next, a delete operation is executed to delete the character string "Bye!" displayed on the first line of the display unit 33. In this case, the command code "remove / text / 1" (see FIG. 2(E)) is executed. As a result, the first line of the data code Cm is deleted, as shown in FIG. 3(E). Also, the character string "Bye!" (see FIG. 3(D)) displayed on the first line of the display unit 33 is deleted, and the display content is updated.

[0031] Furthermore, the instruction code required to restore the updated display content (see FIG. 3(E)) to the display content before the update (see FIG. 3(D)) is determined. Specifically, this is as follows. To restore the updated display content shown in FIG. 3(E) to the display information before the update shown in FIG. 3(D), the character string "Bye!" is added to the first line of the display unit 33 and displayed. Therefore, the instruction code "add / text / 1 "Bye!"" is determined, which includes the command "add", type "text", line "1", and the character string "Bye!". The determined instruction code is newly added to the history information Us. The added instruction code "add / text / 1 "Bye!"" is associated with the operation sequence "004".

[0032] <Display screen 5A> Fig. 4 shows in detail the display screen 5A displayed on the display unit 33 of the display device 3. The display screen 5A includes a main area 51, an operation history area 52, a save button 53, an UNDO button 54, and a REDO button 55. Fig. 4 shows the state after the series of input operations (add operation, add operation, change operation, delete operation) shown in Figs. 3(A) to 3(E) have been executed.

[0033] An image corresponding to an input operation is displayed in the main area 51. The display content of the main area 51 (hereinafter referred to as "latest display content") is specified based on the data code Cm (see FIG. 3) stored in the flash memory 32C. The operation history area 52 displays information indicating a plurality of input operations that have been performed (hereinafter referred to as "input operation items") in the order in which the input operations were performed. The display content of the operation history area 52 is specified based on the data code Ch stored in the flash memory 32C. The data code Ch is determined based on the history information Us.

[0034] In the example shown in Fig. 4, the main area 51 displays only the character string "Hello!" as the latest display content, similar to Fig. 3(E). In addition, the operation history area 52 displays, in order from top to bottom, the following input operation items: "Add 'Hi!'" indicating the operation of adding the character string "Hi!" (see Fig. 3(B)), "Add 'Bye!'" indicating the operation of adding the character string "Bye!" (see Fig. 3(C)), "Change 'Hi!' → 'Hello!'" indicating the operation of changing the character string "Hi" to the character string "Hello!" (see Fig. 3(D)), and "Delete 'Bye!'" indicating the operation of deleting the character string "Bye" (see Fig. 3(E)). The display order of the input operation items corresponds to the order in which the input operations were performed.

[0035] It should be noted that if the user touches and selects any of the input operation items in the operation history area 52 and maintains this state, the selected input operation item can be deleted from the operation history area 52. Hereinafter, this operation will be referred to as a "selection operation."

[0036] The save button 53 is a selection button for saving a file showing the latest display contents in the flash memory 32 C. Hereinafter, the input operation of selecting the save button 53 will be referred to as a “save operation.”

[0037] The UNDO button 54 is a selection button for undoing add operations, change operations, and delete operations in the reverse order of the order in which the input operations were performed. Hereinafter, the input operation of selecting the UNDO button 54 will be referred to as the "UNDO operation." When the UNDO operation is performed, the latest display content in the main area 51 is restored from the display content after the add operation, change operation, or delete operation was performed to the display content before the add operation, change operation, or delete operation was performed.

[0038] In this embodiment, as described above, the command code required to restore the updated display content to the display content before the update is stored as the history information Us. Therefore, the display device 3 can realize the operation of updating the latest display content in the main area 51 in response to an UNDO operation by simply executing the command code stored in the history information Us.

[0039] The REDO button 55 is a selection button for canceling the input operation of selecting the UNDO button 54. Hereinafter, the input operation of selecting the REDO button 55 will be referred to as the "REDO operation." When the REDO operation is executed, the display content of the main area 51 is returned from the display content after the operation of selecting the UNDO button 54 was executed to the display content before the operation of selecting the UNDO button 54 was executed.

[0040] <First flag control process> The first flag control process will be described with reference to FIG. 5. The first flag control process controls a flag for determining the timing to add an instruction code to and update the history information Us. The flag is stored in RAM 32B. The flag is referenced in the first main process (see FIGS. 6 to 8) described below. The first flag control process is started by CPU 31 reading and executing a control program stored in flash memory 32C when an operation for starting an application for displaying display screen 5A is performed via input unit 34. When the first flag control process starts, the flag is 0. Hereinafter, setting the flag to 0 will be referred to as "turning the flag OFF," and setting the flag to 1 will be referred to as "turning the flag ON."

[0041] The CPU 31 determines whether a save operation for the display screen 5A has been detected (S1). If a save operation has been detected (S1: YES), the CPU 31 turns on a flag (S3). The CPU 31 returns the process to S1.

[0042] If the CPU 31 does not detect a save operation (S1: NO), the process proceeds to S5. The CPU 31 determines whether the flag is OFF (S5). If the CPU 31 determines that the flag is ON (S5: NO), the process returns to S1. If the CPU 31 determines that the flag is OFF (S5: YES), the CPU 31 determines whether a second period or more has elapsed in a state where the flag is OFF and no input operation has been detected (S3). If the CPU 31 determines that a second period or more has elapsed in a state where the flag is OFF and no input operation has been detected (S7: YES), the CPU 31 turns the flag ON (S3). The CPU 31 returns the process to S1.

[0043] When the CPU 31 determines that the second period or more has not elapsed while the flag is OFF and no input operation is detected (S7: NO), the CPU 31 returns the process to S1.

[0044] <First main process> The first main processing will be described with reference to Figures 6 to 8. The first main processing is started when the display device 3 is powered on and an operation for starting an application for displaying the display screen 5A is performed via the input unit 34, by the CPU 31 reading and executing a control program stored in the flash memory 32C. The first main processing is executed in parallel with the first flag control processing. When the first main processing starts, the variable i stored in the RAM 32B is set to 0.

[0045] Hereinafter, the display content displayed in the main area 51 of the display screen 5A will be referred to as the "latest display content." The command code for updating the latest display content in response to an input operation will be referred to as the "DO code." The latest display content before being updated by the DO code will be referred to as the "pre-update display content," and the latest display content after being updated by the DO code will be referred to as the "post-update display content." The command code required to restore the post-update display content to the pre-update display content will be referred to as the "UNDO code."

[0046] The CPU 31 determines whether an input operation to the input unit 34 has been detected (S11). If the CPU 31 determines that an input operation has not been detected (S11: NO), the process proceeds to S25. If the CPU 31 detects an input operation (S11: YES), the CPU 31 determines whether the detected input operation is an add operation, a change operation, or a delete operation (S13).

[0047] When the CPU 31 determines that the detected input operation is any one of an add operation, a change operation, and a delete operation (S13: YES), it adds 1 to the variable i to update it (S15). The CPU 31 identifies the DO code corresponding to the detected add operation, change operation, or delete operation (S17). The CPU 31 executes the identified DO code to update the data code Cm and stores it in the flash memory 32C (S19). The CPU 31 updates the latest display content of the main area 51 on the display screen 5A based on the data code Cm stored in the flash memory 32C (S21). The CPU 31 associates the variable i with the DO code and temporarily stores it in the RAM 32B (S23).

[0048] The CPU 31 determines whether the flag stored in the RAM 32B is ON (S25). If the flag is OFF (S25: NO), the CPU 31 returns the process to S11. The CPU 31 repeats the processes of S11 to S23 until the flag is turned ON. During this time, each time an add operation, change operation, or delete operation is accepted, the CPU 31 repeats updating the variable i (S15), identifying the DO code (S17), updating and storing the data code Cm (S19), updating the latest display content (S21), and temporarily storing the DO code (S23).

[0049] When the CPU 31 determines that the flag stored in the RAM 32B is ON (S25: YES), it turns the flag OFF (S27). The CPU 31 acquires the DO code stored in the RAM 32B by the processing of S23. Note that, in the first flag control processing (see FIG. 5), if an input operation to select the save button 53 is detected (S1: YES), or if a second period or more has elapsed without an input operation being detected (S7: YES), the flag is turned ON (S3). Therefore, the CPU 31 acquires the DO code stored in the RAM 32B during the first period from the start timing to the end timing described below. Here, the start timing refers to the time when a second period has elapsed during a period during which no input operation is accepted, or the time when a save operation is detected. The end timing refers to the time when a second period has elapsed during a period during which no input operation is accepted after the start timing, or the time when a save operation is detected after the start timing.

[0050] Based on the acquired DO code and data code Cm, the CPU 31 determines, for each acquired DO code, an UNDO code, which is an instruction code required to restore the updated display content to the pre-update display content (S29). The CPU 31 associates the variable i associated with the DO code referenced when determining the UNDO code with the UNDO code as the operation order, and adds it to and stores it in the history information Us of the flash memory 32C (S31). If multiple DO codes are stored in RAM 32B, the CPU 31 performs the above process for all stored DO codes. Thereafter, the CPU 31 deletes all DO codes stored in RAM 32B.

[0051] The CPU 31 acquires an UNDO code from the history information Us stored in the flash memory 32C. Based on the acquired UNDO code and the data code Cm, the CPU 31 identifies, for each acquired UNDO code, a DO code required to update the pre-update display content to the post-update display content (S33). The CPU 31 updates the data code Ch indicating the display content of the operation history area 52 of the display screen 5A so as to display the input operation items corresponding to the identified DO code in the same order as the operation order associated with the UNDO code referenced when the DO code was identified (S35). The CPU 31 updates the display content of the operation history area 52 of the display screen 5A based on the updated data code Ch (S37). Note that the order of the input operation items displayed in the operation history area 52 corresponds to the operation order of the corresponding input operations. The CPU 31 returns the process to S11.

[0052] When the CPU 31 detects an input operation (S11: YES) and determines that the detected input operation is not an add operation, a change operation, or a delete operation (S13: NO), the CPU 31 proceeds to the process at S41 (see FIG. 7). As shown in FIG. 7, the CPU 31 determines whether the detected input operation is an UNDO operation (S41). When the CPU 31 determines that the detected input operation is an UNDO operation (S41: YES), the CPU 31 proceeds to the process at S43.

[0053] The CPU 31 updates the variable i by subtracting 1 (S43). The CPU 31 selects an UNDO code associated with the operation sequence that matches the variable i from the history information Us stored in the flash memory 32C (S45). The CPU 31 executes the selected UNDO code to update the data code Cm and stores it in the flash memory 32C (S47). The CPU 31 updates the latest display content of the main area 51 on the display screen 5A based on the data code Cm stored in the flash memory 32C (S49). As a result, the latest display content of the main area 51 is restored from the post-update display content to the pre-update display content. Furthermore, the pre-update display content is stored in the flash memory 32C as the data code Cm indicating the latest display content. The CPU 31 returns the process to S11.

[0054] When the CPU 31 determines that the detected input operation is not an UNDO operation (S41: NO), the CPU 31 determines whether the detected input operation is a selection operation (S51). When the CPU 31 determines that the detected input operation is a selection operation (S51: YES), the CPU 31 proceeds to the process of S53.

[0055] The CPU 31 updates the data code Ch stored in the flash memory 32C so that the selected input operation item is deleted from the operation history area 52 of the display screen 5A (S53). The CPU 31 updates the display content of the operation history area 52 based on the updated data code Ch (S55). As a result, the input operation item selected in response to the selection operation is deleted from the operation history area 52.

[0056] The CPU 31 identifies the DO code corresponding to the input operation item deleted from the operation history area 52, and further determines an UNDO code for restoring the updated display content to the pre-update display content based on the identified DO code (S57). The CPU 31 deletes the determined UNDO code from the UNDO codes of the history information Us (S59). The CPU 31 returns the process to S11 (see FIG. 6).

[0057] When the CPU 31 determines that the detected input operation is not a selection operation (S51: NO), the CPU 31 proceeds to S61 (see FIG. 8). As shown in FIG. 8, the CPU 31 determines whether the detected input operation is a REDO operation (S61). When the CPU 31 determines that the detected input operation is a REDO operation (S61: YES), the CPU 31 proceeds to S65.

[0058] The CPU 31 selects an UNDO code associated with the operation sequence that matches the variable i from the history information Us stored in the flash memory 32C (S65). Based on the selected UNDO code, the CPU 31 identifies a DO code required to update the pre-update display content to the post-update display content (S67). The identified DO code corresponds to a command code required to cancel the UNDO operation in accordance with the REDO operation and return the latest display content in the main area 51 to the state before the UNDO operation. The CPU 31 executes the identified DO code to update the data code Cm and store it in the flash memory 32C (S69).

[0059] The CPU 31 updates the latest display content of the main area 51 on the display screen 5A based on the data code Cm stored in the flash memory 32C (S71). As a result, the latest display content of the main area 51 is restored from the pre-update display content updated by the UNDO operation to the post-update display content. The post-update display content is stored in the flash memory 32C as the data code Cm indicating the latest display content. The CPU 31 updates the variable i by adding 1 (S73). The CPU 31 returns the process to S11 (see FIG. 6).

[0060] When the CPU 31 determines that the detected input operation is not a REDO operation (S61: NO), it executes a process according to the input operation (S81) and returns the process to S11 (see FIG. 6).

[0061] <Actions and Effects of the First Embodiment> When the display device 3 receives an UNDO operation (S41: YES), it refers to the history information Us and selects an UNDO code in the reverse order of the operation (S43, S45). By executing the selected UNDO code as is, the display device 3 can execute a function (UNDO function) that cancels the add operation, change operation, and delete operation and restores the original display content. Therefore, the display device 3 can implement the UNDO function without referring to multiple command codes stored in the history information Us, and therefore can implement the UNDO function efficiently.

[0062] When the display device 3 receives an UNDO operation (S41: YES), it executes the UNDO code in the history information Us as is and updates the data code Cm (S47). As a result, the latest display content in the main area 51 of the display screen 5A is restored from the updated display content to the original pre-update display content (S49). Therefore, the user of the display device 3 can cause the display device 3 to execute the UNDO function by performing an UNDO operation via the input unit 34.

[0063] The display device 3 identifies a DO code required to update the pre-update display content to the post-update display content based on the UNDO code in the history information Us (S33). The display device 3 displays the input operation items corresponding to the identified DO code in the operation history area 52 of the display screen 5A in the order of the input operations (S37). Therefore, the user can understand the history of the input operations by visually checking the input operation items displayed in the operation history area 52 in the order of the operations.

[0064] When the display device 3 receives a selection operation for selecting an input operation item displayed in the operation history area 52 (S51: YES), the display device 3 deletes the selected input operation item from the operation history area 52 (S55), and also deletes the corresponding UNDO code from the history information Us (S59). This allows the user to secure the remaining capacity by reducing the storage capacity of the display device 3.

[0065] The display device 3 stores at least one DO code in the RAM 32B based on at least one input operation performed during a first period (S23). The display device 3 determines an UNDO code based on the at least one DO code stored in the RAM 32B (S29) and stores the UNDO code in addition to the history information Us (S31). This allows the display device 3 to reduce the frequency of the process of determining an UNDO code, thereby reducing the processing load on the CPU 31. Furthermore, when a second period has elapsed during which no input operation is accepted, or when a save operation has been performed, the display device 3 can determine an UNDO code and store it in the history information Us.

[0066] When the display device receives an add operation, a change operation, or a delete operation as an input operation (S13: YES), it can determine an UNDO code and update the history information Us.

[0067] <Special Notes on the First Embodiment> The present invention is not limited to the first embodiment and various modifications are possible. In the present invention, the image displayed on the display unit 33 is not limited to a character string, but may be a graphic or the like. The format of the data code Cm is not limited to the JSON format, but may be another format. The display device 3 may manage the latest display content of the main area 51 using data in another format.

[0068] The display device 3 may associate a DO code, which is a command code for updating the latest display content in response to an add operation, a change operation, or a delete operation, with an UNDO code and add it to the history information U. The UNDO code may further be associated with the date and time when the corresponding input operation was performed, comment information accompanying the corresponding input operation, and the like, and added to the history information U.

[0069] The display device 3 may accept an UNDO operation when two or more input operation items are selected in the operation history area 52. In this case, the display device 3 may select two or more corresponding UNDO codes from the history information Us based on the two or more selected input operation items. The display device 3 may execute the two or more selected UNDO codes in the reverse order of input. In this way, the display device 3 may execute an UNDO function that cancels multiple add operations, change operations, and delete operations at once and restores the original display content.

[0070] The input operation items displayed in the operation history area 52 of the display screen 5A may be arranged from bottom to top in the order of operation. The input operation items may be associated with other information in addition to the content of the operation (add / change / delete) and the image to be operated. For example, the input operation items may be associated with the date and time when the input operation was performed. The operation history area 52 may be displayed in response to an operation of selecting the UNDO button 54 or the REDO button 55.

[0071] An upper limit of the number of input operation items that can be displayed in the operation history area 52 may be specified in advance. When the number of input operation items displayed in the operation history area 52 exceeds the upper limit, the display device 3 may leave the upper limit number of input operation items in the order of operation and select and delete the rest. Furthermore, the display device 3 may delete the UNDO code corresponding to the deleted input operation item from the history information Us.

[0072] The timing at which the display device 3 updates the history information Us, in other words, the timing at which the flag is turned ON in the first flag control process, is not limited to that of the first embodiment. For example, the display device 3 may turn ON the flag at a predetermined cycle. Alternatively, the display device 3 may turn ON the flag when the processing load of the CPU 31 falls below a predetermined level. Alternatively, the display device 3 may turn ON the flag when an add operation, a change operation, or a delete operation has been performed a predetermined number of times. The display device 3 may determine an UNDO code and add it to the history information Us each time an add operation, a change operation, or a delete operation is performed.

[0073] Even when an input operation other than an add operation, a change operation, or a delete operation is received, the display device 3 may determine a corresponding UNDO code and add it to the history information U. For example, when an operation such as moving an image displayed in the main area 51, enlarging or reducing the size of the image, changing the color of the image, or changing the format (font) of the image is performed, the display device 3 may determine a corresponding UNDO code and add it to the history information U.

[0074] The data code Cm is an example of the "latest display content" of the present invention. The UNDO code is an example of the "UNDO process" of the present invention. The process of S13 is an example of the "first receiving step" of the present invention. The process of S19 is an example of the "first storing step" of the present invention. The process of S29 is an example of the "first determining step" of the present invention. The process of S31 is an example of the "second storing step" of the present invention. The process of S37 is an example of the "second display step" of the present invention. The process of S41 is an example of the "second receiving step" of the present invention. The process of S49 is an example of the "UNDO step" of the present invention. The process of S47 is an example of the "third storing step" of the present invention. The process of S33 is an example of the "first identifying step" of the present invention. The process of S37 is an example of the "second display step" of the present invention. The process of S51 is an example of the "selecting step" of the present invention. The process of S55 is an example of the "first deleting step" of the present invention. The process of S57 is an example of the "second determining step" of the present invention. The process of S59 is an example of a "second deleting step" of the present invention. The process of S23 is an example of a "fourth storing step" of the present invention.

[0075] The CPU 31 that performs the processing of S13 is an example of the "first receiving means" of the present invention. The CPU 31 that performs the processing of S19 is an example of the "first storage means" of the present invention. The CPU 31 that performs the processing of S29 is an example of the "first determination means" of the present invention. The CPU 31 that performs the processing of S31 is an example of the "second storage means" of the present invention. The display device 3 is an example of the "history management device" of the present invention.

[0076] Second Embodiment The second embodiment differs from the first embodiment in that the server device 2 manages the history information Us instead of the display device 3. Descriptions of configurations and processes common to the first embodiment will be omitted or simplified.

[0077] <Overview of Communication System 1> An overview of the communication system 1 will be described with reference to Fig. 9. The communication system 1 includes a server device 2 and display devices 3A, 3B, and 3C. The server device 2 is communicatively connected to an access point 4A via a network line 4. The display devices 3A, 3B, and 3C each have the same configuration as the display device 3 in the first embodiment (see Fig. 1), and are communicatively connected to the access point 4A wirelessly. The server device 2 and the display devices 3A, 3B, and 3C can communicate with each other via the network line 4 and the access point 4A.

[0078] The users of the display devices 3A, 3B, and 3C are "User A," "User B," and "User C," respectively. User C is the administrator of the communication system 1. Identification information for identifying the user who uses each display device is stored in the flash memory 32C of each of the display devices 3A to 3C. A display screen 5B (see FIG. 11) is displayed on the display unit 33 of the display devices 3A to 3B. Details of the display screen 5B will be described later.

[0079] The server device 2 has a CPU 21, a ROM 22A, a RAM 22B, a flash memory 22C, and a communication I / F 23. The CPU 21 is responsible for overall control of the server device 2. The ROM 22A stores a boot program and setting information. The RAM 22B temporarily stores data while the CPU 21 is executing processing. The flash memory 22C stores a control program to be executed by the CPU 21, data codes Cm and Ch, history information Us, and identification information of a user C who is an administrator of the communication system 1. The communication I / F 23 is a communication module for communicating with the display devices 3A to 3C via the network line 4 and the access point 4A.

[0080] 10, in the communication system 1, a data code Cm indicating the latest display content of the main area 51 of the display screen 5B (see FIG. 11) and a data code Ch indicating the display content of the operation history area 52 are transmitted from the server device 2 to the display devices 3A to 3C (S201). The display devices 3A to 3C receive the data codes Cm and Ch (S203a, S203b, S203c), and update and display the main area 51 and the operation history area 52 of the display screen 5B (S205a, S205b, S205c). As a result, the display screens 5B of the display devices 3A to 3C are shared within the communication system 1.

[0081] Furthermore, when an input operation is performed via the input unit 34, the display devices 3A to 3C transmit input operation data indicating details of the input operation to the server device 2. For example, when an input operation is performed on the display device 3A (S207a), the display device 3A transmits the input operation data to the server device 2 (S209a). Furthermore, when transmitting the input operation data to the server device 2, the display device 3A also transmits identification information of the user A who uses the display device 3A to the server device 2 (S209a).

[0082] The server device 2 receives input operation data and identification information from each display device 3A (S211). The server device 2 updates the data codes Cm and Ch based on the received input operation data (S213). The server device 2 transmits the updated data codes Cm and Ch to the display devices 3A to 3C (S221). The display devices 3A to 3C receive the data codes Cm and Ch (S223a, S223b, S223c), and update and display the main area 51 and the operation history area 52 of the display screen 5B (S225a, S225b, S225c). As a result, even if an input operation is performed on the display device 3A, the display screen 5B updated in response to this input operation is shared among the display devices 3A to 3C.

[0083] 11 shows a display screen 5B displayed on the display unit 33 of the display device 3 in the second embodiment. The difference from the display screen 5A in the first embodiment (see FIG. 4) is that identification information indicating the user of the display device 3 who performed the input operation is associated with the input operation and displayed in the operation history area 52. The main area 51, the save button 53, the undo button 54, and the redo button 55 are the same as those on the display screen 5A in the first embodiment.

[0084] When the received input operation data indicates an add operation, a change operation, or a delete operation, the server device 2 determines, based on the corresponding DO code, an UNDO code required to restore the updated display content to the pre-update display content. As shown in Fig. 10, the server device 2 associates the determined UNDO code with the received identification information and operation order, adds the received identification information to the history information Us, and stores the associated information in the flash memory 22C (S215). That is, in the second embodiment, unlike the first embodiment, identification information is further associated with the UNDO code in the history information Us, and the associated information is stored in the flash memory 22C of the server device 2.

[0085] <Second flag control process> The second flag control process will be described with reference to Fig. 12. The second flag control process is started when the server device 2 is powered on and the CPU 21 reads and executes a control program stored in the flash memory 22C. The flag is stored in the RAM 22B. The flag is referenced in the second main process (see Figs. 13 to 16) described later. When the second flag control process starts, the flag is OFF.

[0086] The CPU 21 determines whether the flag is OFF (S101). If the CPU 21 determines that the flag is ON (S101: NO), the process returns to S101. If the CPU 21 determines that the flag is OFF (S101: YES), the CPU 21 determines whether a second period or more has elapsed while the flag is OFF and no input operation data has been received (S103). If the CPU 31 determines that the second period or more has elapsed while the flag is OFF and no input operation data has been received (S103: YES), the CPU 31 turns the flag ON (S105). The CPU 31 returns the process to S101.

[0087] <Second main process> The second main processing will be described with reference to Figures 13 to 16. The second main processing is started when the server device 2 is powered on and the CPU 21 reads and executes a control program stored in the flash memory 22C. The second main processing is executed in parallel with the second flag control processing. When the second main processing starts, the variable i stored in the RAM 22B is set to 0.

[0088] The CPU 21 determines whether it has received input operation data and identification information transmitted from any of the display devices 3A to 3C (S111). If it has determined that it has not received the input operation data and identification information (S111: NO), the CPU 21 proceeds to the process at S125. If it has received the input operation data and identification information (S111: YES), the CPU 21 determines, based on the received input operation data, whether the input operation performed on the display device 3 is an add operation, a change operation, or a delete operation (S113).

[0089] When the CPU 21 determines that the operation is any one of an addition operation, a change operation, and a deletion operation (S113: YES), it adds 1 to the variable i to update it (S115). The CPU 21 identifies the DO code corresponding to the addition operation, the change operation, or the deletion operation (S117). The CPU 21 executes the identified DO code to update the data code Cm and stores it in the flash memory 22C (S119). The CPU 21 transmits the data code Cm stored in the flash memory 22C to the display devices 3A to 3C (S121). The CPU 21 associates the identification information and the variable i received in the process of S111 with the DO code identified in the process of S117, and temporarily stores them in the RAM 22B (S123).

[0090] The display devices 3A to 3C that have received the data code Cm transmitted in the process of S121 each update and display the latest display content in the main area 51 of the display screen 5B based on the data code Cm.

[0091] The CPU 21 determines whether the flag stored in the RAM 22B is ON (S125). If the flag is OFF (S125: NO), the CPU 21 returns the process to S111. The CPU 21 repeats the processes of S111 to S123 until the flag is turned ON. During this time, each time input operation data indicating an add operation, a change operation, or a delete operation is received from the display device 3, the CPU 21 repeats updating the variable i (S115), identifying the DO code (S117), updating and storing the data code Cm (S119), transmitting the data code Cm (S121), and temporarily storing the DO code (S123).

[0092] When the CPU 21 determines that the flag stored in the RAM 22B is ON (S125: YES), it turns the flag OFF (S127). The CPU 21 acquires the DO code stored in the RAM 22B by the process of S123. In the second flag control process (see FIG. 12), if the second period or more has elapsed without receiving input operation data (S103: YES), the flag is turned ON (S105). Therefore, the CPU 21 acquires the DO code stored in the RAM 22B during the first period from the time when the second period without receiving input operation data has elapsed until the time when the next second period without receiving input operation data has elapsed.

[0093] Based on the acquired DO code and data code Cm, the CPU 21 determines, for each acquired DO code, an UNDO code, which is a command code required to restore the updated display content to the pre-update display content (S129). The CPU 21 associates the variable i associated with the DO code referenced when determining the UNDO code with the UNDO code as the operation order. The CPU 21 also associates the identification information associated with the DO code referenced when determining the UNDO code with the UNDO code. The CPU 21 adds the UNDO code associated with the operation order and the identification information to the history information Us in the flash memory 32C and stores it (S131). If multiple DO codes are stored in the RAM 22B, the CPU 21 performs the above process for all stored DO codes. Thereafter, the CPU 21 deletes all DO codes stored in the RAM 22B.

[0094] The CPU 21 acquires an UNDO code from the history information Us stored in the flash memory 22C. Based on the acquired UNDO code and the data code Cm, the CPU 21 identifies, for each acquired UNDO code, a DO code required to update the pre-update display content to the post-update display content (S133). The CPU 21 updates the data code Ch indicating the display content of the operation history area 52 on the display screen 5B so as to display the input operation item corresponding to the identified DO code and the identification information associated with the UNDO code referenced when identifying the DO code in the same order as the operation order associated with the UNDO code (S135). The CPU 21 transmits the updated data code Ch to the display devices 3A to 3C (S137). The CPU 21 returns the process to S111.

[0095] The display devices 3A to 3C that have received the data code Ch transmitted in the process of S137 each update and display the display content in the operation history area 52 of the display screen 5B based on the data code Ch. As a result, the input operation items are associated with identification information indicating the users of the display devices 3A to 3C who performed the corresponding input operations, and are displayed in the operation history area 52 of the display screen 5B, as shown in Fig. 11. The order of the input operation items and the identification information displayed in the operation history area 52 corresponds to the order of the corresponding input operations.

[0096] When the CPU 21 determines, based on the received input operation data, that the input operation performed on the display device 3 is not any of the add operation, change operation, and delete operation (S113: NO), the CPU 21 proceeds to the process at S141 (see FIG. 14). As shown in FIG. 14, the CPU 21 determines, based on the received input operation data, whether the input operation performed on the display device 3 is an UNDO operation (S141). When the CPU 21 determines that the input operation is an UNDO operation (S141: YES), the CPU 21 proceeds to the process at S143.

[0097] The CPU 21 updates the variable i by subtracting 1 from it (S143). The CPU 21 selects, from the history information Us stored in the flash memory 22C, an UNDO code associated with the operation sequence that matches the variable i, and identification information associated with this UNDO code (S145).

[0098] The CPU 21 determines whether the selected identification information matches the identification information received together with the input operation data indicating the UNDO operation (S301). If the CPU 21 determines that the identification information matches (S301: YES), the process proceeds to S147. The CPU 21 executes the selected UNDO code to update the data code Cm. The CPU 21 stores the updated data code Cm in the flash memory 32C (S147). The CPU 21 transmits the data code Cm stored in the flash memory 22C to the display devices 3A to 3C (S149). As a result, the display content before update is stored in the flash memory 32C as the data code Cm indicating the latest display content. The CPU 21 returns the process to S111 (see FIG. 13).

[0099] The display devices 3A to 3C that have received the data code Cm transmitted by the process of S149 each update and display the latest display content in the main area 51 of the display screen 5B based on the data code Cm. As a result, the latest display content in the main area 51 returns to the display content before being updated to the updated display content by the UNDO operation (pre-update display content).

[0100] When the CPU 21 determines that the identification information associated with the UNDO code selected from the history information Us does not match the identification information received when receiving the input operation data indicating the UNDO operation (S301: NO), the CPU 21 proceeds to S303. The CPU 21 determines whether the identification information received when receiving the input operation data indicating the UNDO operation matches the identification information indicating the administrator of the communication system 1, based on the administrator identification information stored in the flash memory 22C (S303). When the CPU 21 determines that the received identification information matches the identification information indicating the administrator (S303: YES), the CPU 21 proceeds to S147. The processes of S147 and S149 are the same as those when it is determined that the identification information matches, and therefore a description thereof will be omitted.

[0101] If the CPU 21 determines that the received identification information does not match the identification information indicating the administrator of the communication system 1 (S303: NO), it adds 1 to the variable i to restore the variable i updated in S143 (S305). In this case, the processes for restoring the main area 51 of the display screen 5B of the display device 3 from the updated display content to the updated display content (updating the data code Cm (S147) and transmitting (S149)) are not executed. The CPU 21 returns the process to S111 (see FIG. 13).

[0102] When the CPU 21 determines, based on the received input operation data, that the input operation performed on the display device 3 is not an UNDO operation (S141: NO), the CPU 21 proceeds to the process at S151 (see FIG. 15). As shown in FIG. 15, the CPU 21 determines, based on the received input operation data, whether the input operation performed on the display device 3 is a selection operation (S151). When the CPU 21 determines that the input operation is a selection operation (S151: YES), the CPU 21 proceeds to the process at S311.

[0103] Based on the input operation data, the CPU 21 identifies an input operation item selected by a selection operation executed on the display device 3. The CPU 21 identifies a DO code corresponding to the identified input operation item, and further determines an UNDO code for restoring the updated display content to the pre-update display content based on the identified DO code (S311). The CPU 31 selects, from the history information Us, identification information associated with the same UNDO code as the determined UNDO code (S313).

[0104] The CPU 21 determines whether the selected identification information matches the identification information received together with the input operation data indicating the selection operation (S315). If the CPU 21 determines that the identification information matches (S313: YES), the process proceeds to S153. The CPU 21 updates the data code Ch stored in the flash memory 22C so that the input operation item selected by the selection operation is deleted from the operation history area 52 of the display screen 5B (S153). The CPU 21 transmits the updated data code Ch to the display devices 3A to 3C (S155). The CPU 21 also deletes the UNDO code determined by the process of S311 from the history information Us (S159). The CPU 21 returns the process to S111 (see FIG. 13).

[0105] The display devices 3A to 3C that have received the data code Ch transmitted by the process of S155 update and display the display content in the operation history area 52 of the display screen 5B, respectively, based on the data code Ch. As a result, the input operation item selected by the selection operation is deleted from the operation history area 52 of the display screen 5B of each of the display devices 3A to 3C.

[0106] When the CPU 21 determines that the identification information associated with the same UNDO code as the determined UNDO code in the history information Us does not match the identification information received when receiving the input operation data indicating a selection operation (S315: NO), the CPU 21 proceeds to S317. The CPU 21 determines whether the identification information received when receiving the input operation data indicating a selection operation matches the identification information indicating the administrator of the communication system 1, based on the administrator identification information stored in the flash memory 22C (S317). When the CPU 21 determines that the received identification information matches the identification information indicating the administrator (S317: YES), the CPU 21 proceeds to S153. The processes of S153 to S159 are the same as those when it is determined that the identification information matches, and therefore a description thereof will be omitted.

[0107] When the CPU 21 determines that the received identification information does not match the identification information indicating the administrator of the communication system 1 (S317: NO), the process returns to S111 (see FIG. 13). In this case, the processes of deleting the input operation item selected by the selection operation from the operation history area 52 of the display screen 5B of the display device 3 (updating the data code Ch (S153), sending (S155), and updating the history information Us (S159)) are not executed.

[0108] When the CPU 21 determines, based on the received input operation data, that the input operation performed on the display device 3 is not a selection operation (S151: NO), the CPU 21 proceeds to the process at S161 (see FIG. 16). As shown in FIG. 16, the CPU 21 determines, based on the received input operation data, whether the input operation performed on the display device 3 is a REDO operation (S161). When the CPU 21 determines that the input operation is a REDO operation (S161: YES), the CPU 21 proceeds to the process at S165.

[0109] The CPU 21 selects an UNDO code associated with the operation sequence that matches the variable i from the history information Us stored in the flash memory 22C (S165). The CPU 21 identifies a DO code to be executed to update the pre-update display content to the post-update display content based on the selected UNDO code (S167). The CPU 21 updates the data code Cm by executing the identified DO code and stores it in the flash memory 22C (S169). The CPU 21 transmits the data code Cm stored in the flash memory 22C to the display devices 3A to 3C (S171). The CPU 21 updates the variable i by adding 1 (S173). The CPU 21 returns the process to S111 (see FIG. 13).

[0110] The display devices 3A to 3C that have received the data code Cm transmitted by the process of S171 each update and display the latest display content in the main area 51 of the display screen 5B based on the data code Cm. As a result, the latest display content in the main area 51 returns from the pre-update display content updated by the UNDO operation to the post-update display content.

[0111] If the CPU 21 determines, based on the received input operation data, that the input operation performed on the display device 3 is not a REDO operation (S161: NO), it executes processing according to the input operation (S181) and returns the processing to S111 (see Figure 13).

[0112] <Actions and Effects of the Second Embodiment> When the server device 2 receives input operation data indicating an UNDO operation (S141: YES), it refers to the history information Us and selects an UNDO code in the reverse order of the operation (S143, S145). The server device 2 executes the selected UNDO code as is to update the data code Cm (S147) and transmits it to the display device 3 (S149). The display device 3 updates the latest display content in the main area 51 of the display screen 5B from the post-update display content to the pre-update display content based on the data code Cm received from the server device 2. This allows the server device 2 to cause the display device 3 to execute the UNDO function. The server device 2 can cause the display device 3 to execute the UNDO function without referring to the multiple command codes stored in the history information Us, thereby efficiently executing the UNDO function.

[0113] When the server device 2 receives input operation data indicating an UNDO operation (S141: YES), it executes the UNDO code in the history information Us as is and updates the data code Cm (S147). The server device 2 transmits the updated data code Cm to the display device (S149). As a result, the latest display content in the main area 51 of the display screen 5B of the display device 3 is restored from the updated display content to the original pre-update display content. Therefore, the user of the display device 3 can cause the display device 3 to execute the UNDO function by performing an UNDO operation via the input unit 34.

[0114] If the identification information associated with the UNDO code stored as the history information Us matches the identification information received when receiving the input operation data indicating the UNDO operation (S301: YES), the server device 2 executes the UNDO code to update the data code Cm (S147) and transmits the data code Cm to the display device 3 (S149). In this case, the server device 2 can prohibit the latest display content in the main area 51 from being updated from the post-update display content to the pre-update display content when a user other than the user who performed the input operation performs an UNDO operation to cancel the input operation. In other words, the server device 2 can update the latest display content in the main area 51 from the post-update display content to the pre-update display content when the user who performed the input operation performs an UNDO operation to cancel the input operation.

[0115] When the server device 2 receives the input operation data indicating the UNDO operation and also receives identification information that matches the identification information of the administrator of the communication system 1 (S303: YES), it executes the UNDO code to update the data code Cm (S147) and transmits the data code Cm to the display device 3 (S149). In this case, even if a user other than the user who performed the input operation performs the UNDO operation to cancel this input operation, the server device 2 can update the latest display content in the main area 51 from the post-update display content to the pre-update display content if the user is the administrator.

[0116] The server device 2 identifies a DO code required to update the pre-update display content to the post-update display content based on the UNDO code in the history information Us (S133). The server device 2 updates the data code Ch so that the input operation item corresponding to the identified DO code is associated with the identification information of the user who performed the input operation and is displayed in the operation history area 52 of the display screen 5B (S135). The server device 2 transmits the updated data code Ch to the display device 3 (S137). Therefore, the user of the display device 3 can grasp the history of input operations by visually checking the input operation items displayed in the operation history area 52 in the order of operation. The user of the display device 3 can also confirm the user who performed the input operation.

[0117] When the identification information associated with the UNDO code stored as the history information Us matches the identification information received together with the input operation data indicating the selection operation (S315: YES), the server device 2 updates the data code Ch so that the selected input operation item is deleted from the operation history area 52 (S153), and transmits the updated data code Ch to the display device 3 (S155). Furthermore, the server device 2 determines an UNDO code corresponding to the selected input operation item from the history information Us (S311), and deletes it from the history information Us (S159).

[0118] In this case, when a user other than the user who performed the input operation performs a selection operation to delete the UNDO code corresponding to this input operation from the history information Us, the server device 2 can prohibit the input operation item from being deleted from the operation history area 52 and the UNDO code from being deleted from the history information Us. In other words, when the user who performed the input operation performs a selection operation for this input operation, the server device 2 can update the display content of the operation history area 52 and delete the UNDO code from the history information Us.

[0119] <Special Notes on the Second Embodiment> The present invention is not limited to the second embodiment, and various modifications are possible. Note that the modifications described in the first embodiment can also be applied to the second embodiment as appropriate.

[0120] The display device 3 may periodically transmit request data requesting the data codes Cm and Ch to the server device 2. The server device 2 may transmit the data codes Cm and Ch to the display device 3 at the timing when it receives request data from the display device 3. Alternatively, the server device 2 may repeatedly transmit the data codes Cm and Ch to the display device 3 at a predetermined period. The functions of the server device 2 described in the second embodiment may be executed by any one of the display devices 3A to 3C (master display device) instead of the server device 2.

[0121] In the second embodiment, the identification information of the user who uses the display device 3 is transmitted from the display device 3 to the server device 2 together with the input operation data. If the display device 3 used by each user is fixed for each user, the identification information can be said to be identification information that indirectly identifies the display device 3. In contrast, the display device 3 may transmit identification information that directly identifies the display device 3 (for example, the serial number, MAC address, IP address, etc. of the display device 3) to the server device 2 together with the input operation data. The operation history area 52 of the display screen 5B may display the input operation items in association with the identification information that directly identifies the display device 3.

[0122] When the display device 3 receives an UNDO operation for restoring the post-update display content to the pre-update display content, the display device 3 may determine whether an input operation for updating the pre-update display content to the post-update display content has been previously performed via the input unit 34. The display device 3 may transmit input operation data indicating the UNDO operation to the server device 2 only if the input operation has been previously performed. On the other hand, when the input operation has not been previously performed, the display device 3 may not transmit input operation data indicating the UNDO operation to the server device 2 and may prohibit the UNDO function. In other words, the display device 3 may enable the UNDO function only if the user has performed an UNDO operation for undoing an input operation performed by the user.

[0123] The display device 3 may accept an UNDO operation in a state where two or more input operation items are selected in the operation history area 52. In this case, the display device 3 may extract, from the two or more selected input operation items, an input operation item that is an input operation previously performed via the input unit 34. The display device 3 may transmit input operation data indicating an UNDO operation for undoing the input operation corresponding to the extracted input operation item to the server device 2. Meanwhile, the server device 2 may select an UNDO code from the history information Us based on the received input operation data, and execute the selected UNDO code.

[0124] When the display device 3 receives a selection operation for selecting an input operation item in the operation history area 52, the display device 3 may determine whether an input operation corresponding to the selected input operation item has been previously performed via the input unit 34. The display device 3 may extract input operation items corresponding to input operations previously performed via the input unit 34, and transmit input operation data indicating these selection operations to the server device 2. On the other hand, the display device 3 may not transmit input operation data indicating the selection operation for an input operation item corresponding to an input operation not previously performed via the input unit 34 to the server device 2, and may prohibit the server device 2 from deleting the UNDO code from the history information Us. In other words, the display device 3 may delete the selected input operation item from the operation history area 52 only when a selection operation for selecting and deleting an input operation performed by a user is performed by the user.

[0125] The processing of S113 is an example of a "first receiving step" of the present invention. The processing of S119 is an example of a "first storing step" of the present invention. The processing of S129 is an example of a "first determining step" of the present invention. The processing of S131 is an example of a "second storing step" of the present invention. The processing of S137 is an example of a "second displaying step" of the present invention. The processing of S141 is an example of a "second receiving step" of the present invention. The processing of S149 is an example of an "UNDO step" of the present invention. The processing of S147 is an example of a "third storing step" of the present invention. The processing of S133 is an example of a "first identifying step" of the present invention. The processing of S137 is an example of a "second displaying step" of the present invention. The processing of S151 is an example of a "third receiving step" of the present invention. The processing of S155 is an example of a "first deleting step" of the present invention. The processing of S311 is an example of a "second determining step" of the present invention. The processing of S159 is an example of a "second deleting step" of the present invention. The process of S23 is an example of the "fourth storing step" of the present invention.

[0126] The CPU 31 that performs the processing of S113 is an example of the "first receiving means" of the present invention. The CPU 31 that performs the processing of S119 is an example of the "first storage means" of the present invention. The CPU 31 that performs the processing of S129 is an example of the "first determination means" of the present invention. The CPU 31 that performs the processing of S131 is an example of the "second storage means" of the present invention. The server device 2 is an example of the "history management device" of the present invention. [Explanation of symbols]

[0127] 1: Communication Systems 2: Server device 3, 3A, 3B, 3C: Display device 21, 31: CPU 51: Main area 52: Operation history area

Claims

1. a first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; a first specifying step of referring to the history information stored in the storage unit in the second storing step and specifying, based on the UNDO code, an instruction code for updating the pre-update display content to the latest display content; a second display step of displaying the input operations corresponding to the instruction codes identified in the first identification step on the display unit in the order of the operations; A history management program that allows a computer to execute the above.

2. a selection step of selecting one of the input operations displayed on the display unit by the second display step; a first deletion step of deleting the input operation selected in the selection step from the display unit; a second determination step of determining, from the UNDO codes included in the history information, an UNDO code required to restore the display content updated in response to the input operation selected in the selection step to the display content before the update, based on a command code corresponding to the input operation; a second deletion step of deleting the UNDO code determined in the second determination step from the history information stored in the storage unit; 2. The history management program according to claim 1, further comprising:

3. A first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; A history management program for causing a computer to execute the following: The second storing step includes: the UNDO code determined in the first determination step is associated with identification information for identifying the display device that received the input operation in the first reception step and the operation order, and the associated UNDO code is stored in the storage unit as the history information; The UNDO step When the UNDO operation is accepted in the second accepting step, the history information stored in the storage unit is referenced, the UNDO process is executed using the UNDO code selected in the reverse order of the operation order, and the latest display content is restored to the pre-update display content and displayed on the display unit of the display device identified by the identification information associated with the executed UNDO process. A history management program characterized by:

4. A first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; A history management program for causing a computer to execute the following: The second storing step includes: the UNDO code determined in the first determination step is associated with identification information for identifying the display device that received the input operation in the first reception step and the operation order, and the associated UNDO code is stored in the storage unit as the history information; The UNDO step The history information stored in the storage unit is referenced, and if the identification information associated with the UNDO code selected in the reverse order of the operation matches the identification information for identifying the display device that accepted the UNDO operation in the second accepting step, the UNDO process is executed using the selected UNDO code, and the latest display content is restored to the pre-update display content and displayed on the display unit. A history management program characterized by:

5. A first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; A history management program for causing a computer to execute the following: The second storing step includes: the UNDO code determined in the first determination step is associated with identification information for identifying the display device that received the input operation in the first reception step and the operation order, and the associated UNDO code is stored in the storage unit as the history information; The UNDO step If the identification information of the display device that has received the UNDO operation in the second receiving step satisfies a predetermined condition, the history information stored in the storage unit is referenced, the UNDO process is executed using the UNDO code selected in the reverse order of the operation order, and the latest display content is restored to the pre-update display content and displayed on the display unit. A history management program characterized by:

6. The second storing step includes: the UNDO code determined in the first determination step is associated with identification information for identifying the display device that received the input operation in the first reception step and the operation order, and the associated UNDO code is stored in the storage unit as the history information; The second display step includes: The history management program according to claim 1, characterized in that the input operation corresponding to the instruction code identified in the first identification step and the identification information associated with the UNDO code are displayed on the display unit in the order of the operations.

7. a third receiving step of receiving, from the display device, a selection operation for selecting one of the input operations displayed on the display unit by the second display step; a first deletion step of deleting, from the display unit, the input operation selected by the selection operation accepted by the third acceptance step, when the identification information for identifying the display device that accepted the selection operation by the third acceptance step matches the identification information associated with the input operation selected by the selection operation; a second determination step of determining, from the UNDO codes included in the history information, an UNDO code required to restore the display content updated in accordance with the input operation selected by the selection operation accepted in the third acceptance step to the display content before the update, based on a command code corresponding to the input operation; a second deletion step of deleting the UNDO code determined in the second determination step from the history information stored in the storage unit; 7. The history management program according to claim 6, further comprising:

8. The fourth storage step: storing, for a first period, an instruction code corresponding to the input operation received at least once in the first receiving step, in the storage unit; The start timing of the first period is the timing at which a second period has elapsed since the first reception step began, or the timing at which a save operation for saving the display content of the display unit has been received; The end timing of the first period is a timing when the second period has elapsed since the start timing during which the input operation is not accepted by the first accepting step, or a timing when the save operation is accepted since the start timing.

8. The history management program according to claim 1, wherein the history management program is a program for managing a history of a file.

9. The first receiving step receives, as the input operation, an operation for displaying a new image on the display unit; An operation for changing the image displayed on the display unit to another image; and An operation for deleting the image displayed on the display unit 9. The history management program according to claim 1, wherein the program accepts a command.

10. a first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; a first specifying step of referring to the history information stored in the storage unit in the second storing step and specifying, based on the UNDO code, an instruction code for updating the pre-update display content to the latest display content; a second display step of displaying the input operations corresponding to the instruction codes identified in the first identification step on the display unit in the order of the operations; A history management method comprising:

11. a first receiving means for receiving an input operation for updating the display content of the display unit; a first storage means for storing the display content updated in response to the input operation received by the first reception means in a storage unit as the latest display content; a first display means for displaying the latest display content stored in the first storage means on the display unit; a fourth storage means for storing in the storage unit a command code corresponding to the input operation received by the first reception means; a first determination means for determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit by the first display means to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit by the fourth storage means; a second storage means for associating the UNDO code determined by the first determination means with an operation sequence, which is the sequence of the input operations accepted by the first acceptance means, and storing the associated UNDO code in the storage unit as history information; second accepting means for accepting an UNDO operation for restoring the latest display content displayed by the first display means to the pre-update display content; an UNDO means for, when the second accepting means accepts the UNDO operation, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; a first specifying means for referring to the history information stored in the storage unit by the second storage means and specifying, based on the UNDO code, a command code for updating the pre-update display content to the latest display content; a second display means for displaying the input operations corresponding to the command codes identified by the first identification means on the display unit in the order of the operations; A history management device comprising:

12. A first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; Equipped with The second storing step includes: the UNDO code determined in the first determination step is associated with identification information for identifying the display device that received the input operation in the first reception step and the operation order, and the associated UNDO code is stored in the storage unit as the history information; The UNDO step When the UNDO operation is accepted in the second accepting step, the history information stored in the storage unit is referenced, the UNDO process is executed using the UNDO code selected in the reverse order of the operation order, and the latest display content is restored to the pre-update display content and displayed on the display unit of the display device identified by the identification information associated with the executed UNDO process. A history management method characterized by:

13. A first receiving means for receiving an input operation for updating the display content of the display unit; a first storage means for storing the display content updated in response to the input operation received by the first reception means in a storage unit as the latest display content; a first display means for displaying the latest display content stored in the first storage means on the display unit; a fourth storage means for storing in the storage unit a command code corresponding to the input operation received by the first reception means; a first determination means for determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit by the first display means to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit by the fourth storage means; a second storage means for associating the UNDO code determined by the first determination means with an operation sequence, which is the sequence of the input operations accepted by the first acceptance means, and storing the associated UNDO code in the storage unit as history information; second accepting means for accepting an UNDO operation for restoring the latest display content displayed by the first display means to the pre-update display content; an UNDO means for, when the second accepting means accepts the UNDO operation, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; Equipped with The second storage means the UNDO code determined by the first determination means is associated with identification information for identifying the display device that has received the input operation by the first reception means and the operation order, and the associated information is stored in the storage unit as the history information; The UNDO means When the second reception means receives the UNDO operation, the history information stored in the storage unit is referenced, the UNDO process is executed using the UNDO code selected in the reverse order of the operation order, and the latest display content is restored to the pre-update display content and displayed on the display unit of the display device identified by the identification information associated with the executed UNDO process. A history management device characterized by:

14. A first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; Equipped with The second storing step includes: the UNDO code determined in the first determination step is associated with identification information for identifying the display device that received the input operation in the first reception step and the operation order, and the associated UNDO code is stored in the storage unit as the history information; The UNDO step The history information stored in the storage unit is referenced, and if the identification information associated with the UNDO code selected in the reverse order of the operation matches the identification information for identifying the display device that accepted the UNDO operation in the second accepting step, the UNDO process is executed using the selected UNDO code, and the latest display content is restored to the pre-update display content and displayed on the display unit. A history management method characterized by:

15. A first receiving means for receiving an input operation for updating the display content of the display unit; a first storage means for storing the display content updated in response to the input operation received by the first reception means in a storage unit as the latest display content; a first display means for displaying the latest display content stored in the first storage means on the display unit; a fourth storage means for storing in the storage unit a command code corresponding to the input operation received by the first reception means; a first determination means for determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit by the first display means to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit by the fourth storage means; a second storage means for associating the UNDO code determined by the first determination means with an operation sequence, which is the sequence of the input operations accepted by the first acceptance means, and storing the associated UNDO code in the storage unit as history information; second accepting means for accepting an UNDO operation for restoring the latest display content displayed by the first display means to the pre-update display content; an UNDO means for, when the second accepting means accepts the UNDO operation, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; Equipped with The second storage means the UNDO code determined by the first determination means is associated with identification information for identifying the display device that has received the input operation by the first reception means and the operation order, and the associated information is stored in the storage unit as the history information; The UNDO means The history information stored in the storage unit is referenced, and if the identification information associated with the UNDO code selected in the reverse order of the operation matches the identification information for identifying the display device that accepted the UNDO operation by the second accepting means, the UNDO process is executed using the selected UNDO code, and the latest display content is restored to the pre-update display content and displayed on the display unit. A history management device characterized by:

16. A first receiving step of receiving an input operation for updating the display content of the display unit; a first storage step of storing the display content updated in response to the input operation received in the first receiving step in a storage unit as latest display content; a first display step of displaying the latest display content stored in the first storage step on the display unit; a fourth storage step of storing, in the storage unit, an instruction code corresponding to the input operation received in the first reception step; a first determination step of determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit in the first display step to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit in the fourth storage step; a second storage step of associating the UNDO code determined in the first determination step with an operation sequence, which is the sequence of the input operations received in the first reception step, and storing the associated UNDO code in the storage unit as history information; a second receiving step of receiving an UNDO operation for returning the latest display content displayed in the first display step to the pre-update display content; an UNDO step of, when the UNDO operation is accepted by the second accepting step, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; Equipped with The second storing step includes: the UNDO code determined in the first determination step is associated with identification information for identifying the display device that received the input operation in the first reception step and the operation order, and the associated UNDO code is stored in the storage unit as the history information; The UNDO step If the identification information of the display device that has received the UNDO operation in the second receiving step satisfies a predetermined condition, the history information stored in the storage unit is referenced, the UNDO process is executed using the UNDO code selected in the reverse order of the operation order, and the latest display content is restored to the pre-update display content and displayed on the display unit. A history management method characterized by:

17. A first receiving means for receiving an input operation for updating the display content of the display unit; a first storage means for storing the display content updated in response to the input operation received by the first reception means in a storage unit as the latest display content; a first display means for displaying the latest display content stored in the first storage means on the display unit; a fourth storage means for storing in the storage unit a command code corresponding to the input operation received by the first reception means; a first determination means for determining an UNDO code, which is a command code for executing an UNDO process required to restore the latest display content displayed on the display unit by the first display means to the pre-update display content, based on the command code corresponding to the input operation stored in the storage unit by the fourth storage means; a second storage means for associating the UNDO code determined by the first determination means with an operation sequence, which is the sequence of the input operations accepted by the first acceptance means, and storing the associated UNDO code in the storage unit as history information; second accepting means for accepting an UNDO operation for restoring the latest display content displayed by the first display means to the pre-update display content; an UNDO means for, when the second accepting means accepts the UNDO operation, referring to the history information stored in the storage unit, executing the UNDO process using the UNDO code selected in the reverse order of the operation order, and restoring the latest display content to the pre-update display content and displaying the restored content on the display unit; Equipped with The second storage means the UNDO code determined by the first determination means is associated with identification information for identifying the display device that has received the input operation by the first reception means and the operation order, and the associated information is stored in the storage unit as the history information; The UNDO means When the identification information of the display device that has received the UNDO operation by the second receiving means satisfies a predetermined condition, the history information stored in the storage unit is referenced, the UNDO process is executed using the UNDO code selected in the reverse order of the operation order, and the latest display content is restored to the pre-update display content and displayed on the display unit. A history management device characterized by:

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