Distributed XPath Query Evaluation via Partial Result Composition
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Solution Overview
Problem
Existing methods for evaluating XPath filters on fragmented and distributed XML documents result in unbounded network traffic and inefficient processing due to sequential access across multiple sites, as they typically require visiting each site multiple times and shipping data sequentially.
Innovation Solution
The method involves partial evaluation, where each site independently evaluates a query against its fragments in parallel, producing partial results that are then composed to yield the final answer, decoupling dependencies and minimizing network traffic by ensuring each site is visited only once.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If existing XPath evaluation methods are applied to fragmented and distributed XML documents, then the query can be evaluated across distributed sites, but the network traffic becomes unbounded and processing becomes inefficient due to sequential site visits
Solution Approach 1:
The patent segments the XML document into fragments distributed across multiple sites, and correspondingly segments the XPath query evaluation into partial evaluations at each site. Each site evaluates its local fragments independently using partial evaluation techniques, producing partial results that are later composed. This segmentation eliminates the need to ship entire documents across the network and enables parallel processing at distributed sites.
Solution Approach 2:
The patent performs preliminary actions by pre-evaluating XPath queries at each distributed site on local fragments before composition. The partial evaluation at each site prepares intermediate results in advance, which are then combined at the coordinating site. This preliminary action at each site avoids the need for multiple sequential visits and reduces overall network traffic by localizing the evaluation work.
2Adaptability or versatility
If existing XPath evaluation methods are applied to fragmented and distributed XML documents, then the query can be evaluated across distributed sites, but the processing efficiency deteriorates due to sequential access and multiple site visits
Solution Approach 1:
The patent divides the query evaluation task into independent segments that can be executed in parallel at different sites. Each site performs partial evaluation on its local fragments simultaneously, rather than waiting for sequential processing. The partial results are then composed at the coordinating site, achieving productivity improvement through parallel execution while maintaining adaptability to distributed document structures.
Solution Approach 2:
The patent performs preliminary partial evaluation at each distributed site before composition, preparing intermediate results in parallel. This preliminary action eliminates the need for multiple sequential site visits, as each site completes its evaluation work in advance. The composition phase then efficiently combines these pre-prepared partial results, significantly improving processing efficiency compared to sequential approaches.
3Ease of operation
If data is shipped from one site to another in existing methods, then query evaluation can proceed, but network traffic increases heavily
Solution Approach 1:
The patent extracts only the necessary partial results from each distributed site rather than shipping entire document fragments. The partial evaluation at each site extracts intermediate results that are sufficient for composition, eliminating the need to transfer large amounts of data across the network. This extraction approach maintains query evaluation capability while dramatically reducing network traffic.
Solution Approach 2:
The patent introduces partial results as intermediaries between the distributed fragments and the final query answer. Instead of directly shipping and processing entire document fragments across the network, the system uses compact partial evaluation results as intermediary representations. These intermediaries can be efficiently composed at the coordinating site to produce the final answer, reducing network traffic while preserving ease of operation.
Data Source
AI summary
Methods and apparatus are provided for evaluating XPath filters on fragmented and distributed XML documents. According to one aspect of the invention, a method is disclosed for evaluating a query over a tree having a plurality of fragments distributed over a plurality of sites. The method comprises the steps of identifying the plurality of sites storing at least one of the plurality of fragments of the tree; providing the query to the plurality of identified sites, wherein each of the identified sites partially evaluates the query against one of more fragments of the tree stored by the respective site; obtaining partial results from the plurality of identified sites; and composing the partial results to compute a result to the query. The query may be, for example, a boolean XPath query. The method can be performed, for example, by a coordinating site that stores a root fragment of the tree.