Atmospheric scientific data transmission method and system based on HDFS

Abstract

The invention discloses an HDFS (Hadoop Distributed File System)-based atmospheric science data transmission method and system, and relates to the technical field of computer application, and the method comprises the following steps: a user client sends a data access request to a data access protocol converter; the data access protocol converter converts the data access request into a query instruction and sends the query instruction to the back-end program client; the back-end program client sends a query instruction to the back-end program server; the back-end program server obtains a query result from the distributed file system according to the query instruction, and sends the query result to the back-end program client; the back-end program client performs protocol conversion processing on the query result to obtain a processing result; and sending the processing result to the user client. According to the invention, data storage and management are more convenient, and the difficulty of data sharing is reduced.

Description

[0001] This application is a divisional application. The application number of the original application is 202111233500.6, the application date is October 22, 2021, and the name of the invention is “A data transmission method and system”. Technical Field

[0002] The present application relates to the field of computer application technology, and more specifically, to an atmospheric science data transmission method and system based on HDFS. Background Art

[0003] Atmospheric science data are mostly stored in Network Common Data Form (NetCDF) or Hierarchical Data Format (HDF). As a self-describing binary data format, this type of file is mostly used for grid data storage in atmospheric science. With the improvement of the accuracy of various meteorological or ocean numerical models and the increase in observation methods and observation points, the volume of atmospheric science data is showing a growing trend. Therefore, data storage needs to provide a sufficient and highly scalable storage environment for atmospheric environmental data, while providing a reliable redundant backup strategy for the data. On the other hand, since NetCDF and HDF files provide a very flexible framework, their formats can be defined by users according to their needs, and the lack of uniformity between data increases the difficulty of transmission and sharing.

[0004] Hadoop is a very successful distributed system framework in the industrial field. It is an open source implementation of the Java version of Google's file system (Google File System, GFS). Hadoop has reliable solutions for data redundancy backup, distributed cluster node management, load balancing and other issues. The framework contains two important components, one of which is the Hadoop Distributed File System (Hadoop Distributed File System, HDFS).

[0005] The open-source project for a Network Data Access Protocol (OPeNDAP) is a data transmission protocol widely used in the field of atmospheric science and is an extension of the HTTP protocol. Structured numerical data stored in cloud or local HDF, NetCDF and other data files can be accessed online through the Internet through this protocol. OPeNDAP establishes a common data model (Common Data Model, CDM) for structured numerical data, which can improve the efficiency and flexibility of data access to data at specific time and space points in the data set.

[0006] The OPeNDAP research organization has developed a parsing program for the protocol, Hyrax. However, Hyrax does not support docking with HDFS. Although the back-end program server (BES) provides an interface for accessing the remote file system, its front-end service (OLFS) does not have a clear interface for users to access the remote file system. In addition, Hyrax needs to index the data directory. For remote file systems, an XML-formatted index file needs to be added to each directory of the original data to indicate the content in the current directory, so that OLFS can correctly return the data source directory page. In other words, when there are file additions and deletions in the file system, these index files need to be dynamically updated. However, in order to avoid problems caused by concurrent writing, HDFS does not support file modification, so it can only be updated by deleting old indexes and adding new indexes. Frequent file operations will lead to frequent index addition and deletion operations, which are very cumbersome and occupy system resources and reduce efficiency. Summary of the invention

[0007] In order to solve the above problems, this application proposes an atmospheric science data transmission method and system based on HDFS.

[0008] In a first aspect, the present application provides an atmospheric science data transmission method based on HDFS, the transmission method comprising:

[0009] The user client sends a data access request to the Data Access Protocol (DAP) converter;

[0010] The DAP converter converts the data access request into a query instruction, and sends the query instruction to a back-end program (Back End Server, BES) client;

[0011] The BES client sends the query instruction to the BES server; the BES server obtains the query result in HDFS according to the query instruction, and sends the query result to the BES client;

[0012] The BES client performs protocol conversion processing on the query result to obtain a processing result;

[0013] The processing result is sent to the user client.

[0014] Preferably, the DAP converter converts the data access request into a query instruction including:

[0015] The data access request is parsed to obtain several parameters in the data access request; the query instruction is generated according to the several parameters in accordance with the specified grammatical rules; the query instruction includes a query instruction fragment corresponding to each parameter in the several parameters.

[0016] Preferably, the BES client sends the query instruction to the BES server; the BES server obtains the query result according to the query instruction, and sends the query result to the BES client, including:

[0017] The BES client establishes a point-to-point transmission protocol with the BES server;

[0018] The BES client sends the query instruction to the BES server via the point-to-point transmission protocol;

[0019] The BES server obtains the query result according to the query instruction, and sends the query result to the BES client;

[0020] The BES client receives and processes the query result.

[0021] Preferably, the BES client and the BES server establish a point-to-point transmission protocol including:

[0022] The BES client sends a transmission control protocol connection request to the BES server;

[0023] The BES server accepts the request and establishes a transmission control protocol connection;

[0024] The BES client sends a connection request to the BES server to apply for establishing a point-to-point transmission protocol; wherein the connection request includes an identifier representing a request for a point-to-point protocol connection;

[0025] The BES server receives the connection request and returns an identifier to the BES client to determine the request result.

[0026] In a second aspect, the present application provides an atmospheric science data transmission system based on HDFS, the transmission system comprising:

[0027] A user client, used to send a data access request to the DAP converter;

[0028] A DAP converter, used for converting the data access request into a query instruction, and sending the query instruction to the BES client;

[0029] BES client, used to send the query instruction to the BES server;

[0030] A BES server is used to obtain query results according to the query instruction and send the query results to the BES client;

[0031] The BES client is also used to perform protocol conversion processing on the query result to obtain a processing result;

[0032] The DAP converter is also used to send the processing result to the user client.

[0033] Preferably, converting the data access request into a query instruction comprises:

[0034] The data access request is parsed to obtain several parameters in the data access request; the query instruction is generated according to the several parameters in accordance with the specified grammatical rules; the query instruction includes a query instruction fragment corresponding to each parameter in the several parameters.

[0035] Preferably, the BES client sends the query instruction to the BES server; the BES server obtains the query result according to the query instruction, and sends the query result to the BES client, including:

[0036] The BES client establishes a point-to-point transmission protocol with the BES server;

[0037] The BES client sends the query instruction to the BES server via the point-to-point transmission protocol;

[0038] The BES server obtains the query result according to the query instruction, and sends the query result to the BES client;

[0039] The BES client receives and processes the query result.

[0040] Preferably, the BES client and the BES server establish a point-to-point transmission protocol including:

[0041] The BES client sends a transmission control protocol connection request to the BES server;

[0042] The BES server accepts the request and establishes a transmission control protocol connection;

[0043] The BES client sends a connection request to the server to apply for establishing a point-to-point transmission protocol; wherein the connection request includes an identifier representing the request for a point-to-point protocol connection;

[0044] The BES server receives the connection request and returns an identifier to the BES client to determine the request result.

[0045] In a third aspect, the present application provides a computing device, comprising a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed by the processor, a pipeline digital management method is executed.

[0046] In a fourth aspect, the present application provides a computer-readable storage medium, comprising computer-readable instructions, which, when a computer reads and executes the computer-readable instructions, enables the computer to execute a pipeline digital management method.

[0047] The present invention proposes a data transmission method and system, which solves the problem that Hyrax does not support docking with HDFS, can make data storage and management more convenient, and reduce the difficulty of data sharing.

[0048] Description of the attached drawings

[0049] In order to more clearly illustrate the technical solutions of the embodiments of this specification, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 This is a schematic diagram of the application of the technical solution provided in the embodiments of the present application;

[0051] Figure 2 A schematic diagram of the method provided in the embodiments of the present application;

[0052] Figure 3 A schematic diagram of a data access protocol converter provided in an embodiment of the present application;

[0053] Figure 4 A schematic diagram of a system provided in an embodiment of the present application;

[0054] Figure 5 A schematic diagram of the structure of a computer device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] To facilitate understanding of the embodiments of the present invention, specific embodiments will be further explained below in conjunction with the accompanying drawings. The embodiments do not constitute a limitation on the embodiments of the present invention.

[0057] Figure 1 This is a schematic diagram of the application of the technical solution provided in the embodiment of this application. Figure 1 As shown, the user can input the data to be queried. The query method of this solution can combine the OPeNDAP protocol and HDFS through the two interfaces of dap and gateway, and can query the data stored on HDFS. In addition, it should be noted that in this application, the atmospheric environment data is mainly used as an example for description. It can be understood that the atmospheric environment data can be equivalently replaced by data in various other possible business scenarios.

[0058] Figure 2 Schematic diagram of the method provided in the embodiment of this application. Figure 2 As shown, in a possible embodiment, the data transmission method of the present application includes:

[0059] S201: The user client sends a data access request to the DAP converter.

[0060] In a possible implementation, the data access request sent by the user client to the DAP converter is a URL request. The specific format is:

[0061] http: / / <hostname> : <port> / <space> / <path> . <type> ？ <constraints>

[0062] Among them, hostname identifies the requested IP address, port identifies the requested port, space identifies the data access method, which can include local access and remote access, path identifies the access path of atmospheric science data on HDFS, and constraints identifies the parameters required to perform the operation.

[0063] For example, a request format sent by a user client can be specifically exemplified as follows:

[0064] http: / / 192.168.1.1:10000 / gateway / nc / data / hello.nc.nc?pm25[0:1:443][0:1:381]

[0065] Among them, 192.168.1.1 corresponds to the format <hostname>; 10000 corresponds to the format <port>; Gateway corresponds to the format <space>; / nc / data / hello.nc corresponds to the format <path>;.nc corresponds to the format <type>;pm25[0:1:443][0:1:381] corresponds to the format <constraints>This request means: remotely access the hello.nc file in the directory / nc / data on HDFS and extract all data in the range [0,441][0,381] in the pm25 variable.

[0066] S202: The DAP converter converts the data access request into a query instruction, and sends the query instruction to the BES client;

[0067] Figure 3 This is a schematic diagram of a DAP converter provided in an embodiment of the present application. Please refer to Figure 3 In a possible implementation manner, the DAP converter converts the data access request into a query instruction including:

[0068] The data access request is parsed by a URL parser to obtain several parameters in the data access request; a query instruction is generated according to the several parameters and in accordance with the prescribed grammatical rules; the query instruction includes a query instruction fragment corresponding to each of the several parameters. The generated query instruction is in XML format.

[0069] For example, convert a specific request http: / / 192.168.1.1:10000 / gateway / nc / data / hell o.nc.nc?pm25[0:1:443][0:1:381] into a query instruction, and the generated query instruction part format is as follows:

[0070]

[0071] Wherein, gateway corresponds to space = "gateway" in the instruction;

[0072] / nc / data / hello.nc corresponds to the resourceID in the instruction;

[0073] .nc corresponds to the returnType in the command;

[0074] pm25[1:0:443][1:0:381] corresponds to the constraintExpression in the instruction.

[0075] The above command means: remotely access the hello.nc file in the directory / nc / data on HDFS, extract all data in the range [0,441][0,381] in the pm25 variable, and return it in the format of a netcdf file.

[0076] S203: The BES client sends a query instruction to the BES server; the BES server obtains the query result on the HDFS according to the query instruction, and sends the query result to the BES client.

[0077] The BES client sends the query instruction in XML format to the BES server. The BES server first accesses the hello.nc file through Gateway according to the resourceID in the query instruction, then extracts the data to be queried according to the constraintExpression, converts the extracted data into the data format .nc corresponding to the returnType, generates the query results, and returns the query results to the BES client.

[0078] Specifically, the BES server obtains the query results in HDFS according to the query instructions. This application can access and obtain files on HDFS through an HTTP request in the following format:

[0079] http: / / <hostname> : <port> / <operation> / <path> ？ <params>

[0080] Among them, hostname represents the host path of HDFS, port represents the port of HDFS, operarion represents the access operation, the parameters include download (representing obtaining data) and upload (representing uploading data), path represents the access path of atmospheric environment data on HDFS, and params represents the parameters required to perform the operation.

[0081] The Gateway interface is used to process the request. The Gateway interface includes Routers, Services, and HDFS clients. Routers are responsible for distributing requests, Services are responsible for parsing parameters and sending them to the HDFS client, and the HDFS client is responsible for receiving parameters and responding according to the parameters, and returning the response results to the BES server.

[0082] In a possible implementation, the BES client sends a query instruction to the BES server including:

[0083] S2031: The BES client establishes a point-to-point transmission protocol with the BES server.

[0084] The BES server is an independently running service program of C / S architecture. After running, it waits to receive the query instruction sent by the BES client, queries the data according to the query instruction and returns the query result to the BES client.

[0085] In a more specific embodiment, the BES client and the BES server establish a point-to-point transmission protocol including:

[0086] S20311: The BES client sends a transmission control protocol connection request to the BES server.

[0087] S20312: The BES server accepts the request and a transmission control protocol connection is established.

[0088] In a more specific embodiment, the BES server sets the SSL security protocol and encrypted transmission, and the BES server requires the BES client to provide verification information. When the verification information is passed, the transmission control protocol connection is established. When the verification information connection times out or the verification fails, the BES client will exit directly, and the transmission control protocol connection establishment fails.

[0089] S20313: The BES client sends a connection request to the BES server to apply for establishing a point-to-point transmission protocol; wherein the connection request includes an identifier representing the request for a point-to-point protocol connection. Table 1 shows the information and description of the identifier.

[0090] Table 1

[0091]

[0092]

[0093] S20314: The BES server receives the connection request and returns an identifier to the BES client to confirm the request result.

[0094] For example, the BES client sends a request containing the identifier "PPTCLIENT_TESTING_CONNE CTION" to the BES server to apply for establishing a PPT protocol connection. After receiving the request, the BES server returns an identifier to indicate the request result based on its own status. When the returned identifier is "PPTSERVER_CONNECTION_OK", it means that the BES server accepts the request and can perform PPT protocol transmission; when the returned identifier is "PPT_PROTOCOL_UNDEFINED", it means that the BES server is busy and the protocol is unavailable; when the returned identifier is "PPTSERVE R_AUTHENTICATE", it means that the BES server has set the SSL security protocol and needs to enter the verification stage.

[0095] S2032: The BES client sends the query instruction to the BES server via the point-to-point transmission protocol.

[0096] Specifically, the BES client transmits the query instruction in XML format to the BES server through the PPT protocol.

[0097] S204: The BES client performs protocol conversion processing on the query result to obtain a processing result; and sends the processing result to the user client.

[0098] Exemplarily, the BES client converts the data returned by the BES server into the data format .nc corresponding to the returnType to generate a query result, and then returns the query result to the user client.

[0099] This application combines the OPeNDAP protocol and HDFS storage through the two interfaces of dap and gateway. This can not only give full play to the advantages of the OPeNDAP protocol and efficiently and conveniently transmit atmospheric environmental data, but also enjoy the management advantages of HDFS such as data redundancy backup.

[0100] Figure 4 Schematic diagram of the system provided in the embodiment of this application. Figure 4 As shown, in a possible embodiment, the data transmission system of the present application includes:

[0101] The user client 401 is used to send a data access request to the DAP converter;

[0102] A data access protocol converter 402 is used to convert a data access request into a query instruction and send the query instruction to a backend program client 403;

[0103] In some possible embodiments, converting a data access request into a query instruction includes:

[0104] The data access request is parsed to obtain several parameters in the data access request; a query instruction is generated according to the several parameters and in accordance with the prescribed grammatical rules; the query instruction includes a query instruction fragment corresponding to each of the several parameters.

[0105] The backend program client 403 is used to send a query instruction to the backend program server 404;

[0106] The backend program server 404 is used to obtain the query result according to the query instruction and send the query result to the backend program client 403;

[0107] In some possible embodiments, the backend program client 403 sends a query instruction to the backend program server 404; the backend program server 404 obtains a query result according to the query instruction, and sends the query result to the backend program client 403, including:

[0108] The backend program client 403 establishes a point-to-point transmission protocol with the backend program server 404;

[0109] In some possible embodiments, the backend program client 403 sends a transmission control protocol connection request to the backend program server 404;

[0110] The backend program server 404 accepts the request and the transmission control protocol connection is established;

[0111] The backend program client 403 sends a connection request to the backend program server 404 to apply for establishing a point-to-point transmission protocol; wherein the connection request includes an identifier representing the request for a point-to-point protocol connection;

[0112] The backend program server 404 receives the connection request and returns an identifier to the backend program client 403 to confirm the request result.

[0113] The backend program client 403 sends the query instruction to the backend program server 404 via the point-to-point transmission protocol;

[0114] The backend program server 404 obtains the query result on the distributed file system 405 according to the query instruction, and sends the query result to the backend program client 403;

[0115] The backend program client 403 receives and processes the query result.

[0116] The backend program client 403 is also used to perform protocol conversion processing on the query result to obtain a processing result; and send the processing result to the user client 401.

[0117] Figure 5 The schematic diagram of the structure of a computer device provided in an embodiment of the present specification is shown, and the computer device may include: a processor 510, a memory 520, an input / output interface 530, a communication interface 540 and a bus 550. The processor 510, the memory 520, the input / output interface 530 and the communication interface 540 are connected to each other in the device through the bus 550. The computer device can be used to perform the above Figure 2 The method shown.

[0118] The processor 510 can be implemented by a general-purpose CPU (Central Processing Unit), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this specification.

[0119] The memory 520 can be implemented in the form of ROM (Read Only Memory), RAM (Random Access Memory), static storage device, dynamic storage device, etc. The memory 520 can store an operating system and other application programs. When the technical solutions provided in the embodiments of this specification are implemented by software or firmware, the relevant program codes are stored in the memory 520 and are called and executed by the processor 510.

[0120] The input / output interface 530 is used to connect the input / output module to realize information input and output. The input / output module can be configured in the device as a component (not shown in the figure), or it can be externally connected to the device to provide corresponding functions. The input device may include a keyboard, a mouse, a touch screen, a microphone, various sensors, etc., and the output device may include a display, a speaker, a vibrator, an indicator light, etc.

[0121] The communication interface 540 is used to connect a communication module (not shown) to realize communication interaction between the device and other devices. The communication module can realize communication through a wired mode (such as USB, network cable, etc.) or a wireless mode (such as mobile network, WIFI, Bluetooth, etc.).

[0122] The bus 550 comprises a pathway that transmits information between the various components of the device (eg, the processor 510 , the memory 520 , the input / output interface 530 , and the communication interface 540 ).

[0123] It should be noted that, although the above device only shows the processor 510, the memory 520, the input / output interface 530, the communication interface 540 and the bus 550, in the specific implementation process, the device may also include other components necessary for normal operation. In addition, it can be understood by those skilled in the art that the above device may also only include the components necessary for implementing the embodiments of the present specification, and does not necessarily include all the components shown in the figure.

[0124] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0125] A person skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware or by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a disk or an optical disk, etc.

[0126] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.< / params> < / path> < / operation> < / port> < / hostname> < / constraints> < / type> < / path> < / space> < / port> < / hostname> < / constraints> < / type> < / path> < / space> < / port> < / hostname>

Claims

1. A method for transmitting atmospheric science data based on HDFS, characterized in that: The transmission method comprises: The user client sends a data access request to the data access protocol converter; The data access protocol converter converts the data access request into a query instruction and sends the query instruction to the backend program client; The backend program client sends a query instruction to the backend program server; the backend program server obtains the query result in the distributed file system according to the query instruction and sends the query result to the backend program client; The backend program client performs protocol conversion processing on the query results to obtain the processing results; Send the processing results to the user client; Among them, the backend program client and the backend program server establish a point-to-point transmission protocol, including: The backend program client sends a transmission control protocol connection request to the backend program server; the backend program server accepts the request and the transmission control protocol connection is established; the backend program client sends a connection request to the backend program server to apply for establishing a point-to-point transmission protocol; wherein the connection request includes an identifier representing the request for a point-to-point protocol connection; the backend program server receives the connection request and returns the identifier to the backend program client to confirm the request result.

2. The atmospheric science data transmission method based on HDFS according to claim 1, characterized in that: The data access protocol converter converts data access requests into query instructions, including: The data access request is parsed to obtain several parameters in the data access request; a query instruction is generated according to the several parameters and in accordance with the prescribed grammatical rules; the query instruction includes a query instruction fragment corresponding to each of the several parameters.

3. The atmospheric science data transmission method based on HDFS according to claim 1, characterized in that: The backend program client sends a query instruction to the backend program server. The backend program server obtains the query result in the distributed file system according to the query instruction and sends the query result to the backend program client, including: The backend program client sends the query instruction to the backend program server via the point-to-point transmission protocol; The backend program server obtains the query results according to the query instruction and sends the query results to the backend program client; The backend program client receives and processes the query results.

4. The atmospheric science data transmission method based on HDFS according to claim 1, characterized in that: The data access request is a URL request, and the query instruction is in XML format.

5. The atmospheric science data transmission method based on HDFS according to claim 1, characterized in that: The data is atmospheric environment data. The OPeNDAP protocol and HDFS are combined together through the two interfaces of dap and gateway to query the data stored on HDFS.

6. An atmospheric science data transmission system based on HDFS, characterized in that: The transmission system comprises: A user client, used for sending a data access request to the data access protocol converter; A data access protocol converter, used to convert data access requests into query instructions and send the query instructions to the backend program client; The backend program client is used to send query instructions to the backend program server; The backend program server is used to obtain query results according to the query instructions and send the query results to the backend program client; The back-end program client is also used to perform protocol conversion processing on the query results to obtain processing results; and send the processing results to the user client; Among them, the backend program client and the backend program server establish a point-to-point transmission protocol, including: The back-end program client sends a transmission control protocol connection request to the back-end program server; the back-end program server accepts the request and the transmission control protocol connection is established; the back-end program client sends a connection request to the server to apply for establishing a point-to-point transmission protocol; wherein the connection request includes an identifier representing the request for a point-to-point protocol connection; the back-end program server receives the connection request and returns the identifier to the back-end program client to confirm the request result.

7. The atmospheric science data transmission system based on HDFS according to claim 6, characterized in that: Convert data access requests into query instructions, including: The data access request is parsed to obtain several parameters in the data access request; a query instruction is generated according to the several parameters and in accordance with the prescribed grammatical rules; the query instruction includes a query instruction fragment corresponding to each of the several parameters.

8. The atmospheric science data transmission system based on HDFS according to claim 6, characterized in that: The backend program client sends a query instruction to the backend program server; the backend program server obtains the query result according to the query instruction and sends the query result to the backend program client, including: The backend program client sends the query instruction to the backend program server via the point-to-point transmission protocol; The backend program server obtains the query results according to the query instruction and sends the query results to the backend program client; The backend program client receives and processes the query results.

9. The atmospheric science data transmission system based on HDFS according to claim 6, characterized in that: The data access request is a URL request, and the query instruction is in XML format.

10. The atmospheric science data transmission system based on HDFS according to claim 6, characterized in that: The data is atmospheric environment data. The OPeNDAP protocol and HDFS are combined together through the two interfaces of dap and gateway to query the data stored on HDFS.

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