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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.
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.
The "/" operator is generalized in XPath 2.0 to allow any kind of expression to be used as an operand: in XPath 1.0, the right-hand side was always an axis step. For example, a function call can be used on the right-hand side. The typing rules for the operator require that the result of the first operand is a sequence of nodes.
The XPath Data Model is a long specification, and goes into many features unrelated to XML trees. Listed below are key terms from that specification and the XML specification. [3] [4] Instance The data model represented as a sequence. Instance document A document using and conforming to the same sequence/XML tree. Sequence
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).
The language is based on XPath 2.0. XQuery programs cannot have side-effects, just like XSLT and provides almost the same capabilities (for instance: declaring variables and functions, iterating over sequences, using W3C schema types), even though the program syntax are quite different. XQuery is logic driven, using FOR, WHERE and function ...
XQuery (XML Query) is a query and functional programming language that queries and transforms collections of structured and unstructured data, usually in the form of XML, text and with vendor-specific extensions for other data formats (JSON, binary, etc.).
Here the XPath //book is evaluated to create a sequence (aka list); the where clause is a functional "filter", the order by sorts the result, and the <shortBook>...</shortBook> XML snippet is actually an anonymous function that builds/transforms XML for each element in the sequence using the 'map' approach found in other functional languages.