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XPath (XML Path Language) is an expression language designed to support the query or transformation of XML documents. It was defined by the World Wide Web Consortium (W3C) in 1999, [1] and can be used to compute values (e.g., strings, numbers, or Boolean values) from the content of an XML document.
For instance, the XML document and the ASCII tree have the same structure. XML Trees do not show the content in an Instance document, only the structure of the document. In this example Product is the Root Element of the tree and the two child nodes of Product are Name and Details. Details contains two child nodes, Description and Price.
Compared to XPath 2.0, XPath 3.0 adds the following new features: . Inline function expressions Anonymous functions can be created in an expression context. For example, the expression function ($ a as xs:double, $ b as xs:double) as xs:double {$ a * $ b} creates a function that returns the product of its two arguments.
Because of the changes in the data model and type system, not all expressions have exactly the same effect in XPath 2.0 as in 1.0. The main difference is that XPath 1.0 was more relaxed about type conversion, for example comparing two strings ( "4" > "4.0" ) was quite possible but would do a numeric comparison; in XPath 2.0 this is defined to ...
Originally, it was based on the XPath 1.0 data model which in turn is based on the XML Information Set. The XDM consists of flat sequences of zero or more items which can be typed or untyped, and are either atomic values or XML nodes (of seven kinds: document, element, attribute, text, namespace, processing instruction, and comment).
XMLStarlet is a set of command line utilities (toolkit) to query, transform, validate, and edit XML documents and files using a simple set of shell commands in a way similar to how it is done with UNIX grep, sed, awk, diff, patch, join, etc commands.
A processing instruction (PI) is an SGML and XML node type, which may occur anywhere in a document, intended to carry instructions to the application. [1] [2]Processing instructions are exposed in the Document Object Model as Node.PROCESSING_INSTRUCTION_NODE, and they can be used in XPath and XQuery with the 'processing-instruction()' command.
XQuery contains a superset of XPath expression syntax to address specific parts of an XML document. It supplements this with a SQL -like " FLWOR expression" for performing joins. A FLWOR expression is constructed from the five clauses after which it is named: FOR, LET, WHERE, ORDER BY, RETURN.