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Early evaluation of XPath expressions using publish and subscribe with XML projection

IP.com Disclosure Number: IPCOM000213521D
Publication Date: 2011-Dec-20
Document File: 1 page(s) / 56K

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The IP.com Prior Art Database


This invention proposes a mechanism that combines a publish/subscribe engine with an XPath evaluation engine so as to optimise the evaluation of multiple XPath expressions without compromising either code structure or performance.

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Early evaluation of XPath expressions using publish and subscribe with XML projection

The XPath language is very commonly used as a means of processing XML data. Typically, an implementation of the XPath language will operate on an XML Info Set. An info set is an in-memory representation of the XML document. It is usual for an XPath processor to load the entire document into memory but this is not practical when the document is very large, and in any case it may not be desirable if memory usage needs to be minimised.

    This invention assumes that one or more XPath expressions need to be evaluated, and the application needs to know the result of the XPath expression evaluations at the earliest opportunity.

    Clearly, it is possible to drive the parsing of the document directly from the XPath processor, so that the evaluation of one XPath expression triggers incremental parsing of the document. This strongly couples the XPath evaluation engine to the XML parser which may not be desirable if the application has other reasons for parsing the XML document besides the evaluation of that single XPath expression.

    A scheme is proposed in which the inputs to all of the XPath expressions are defined as topics in a publish/subscribe engine. As new inputs are published by the XML processor the corresponding expressions are attempted or re-attempted until they succeed. This approach decouples document parsing from expression evaluation and offers a number of advantages in program...