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The XPath syntax is designed to mimic URI (Uniform Resource Identifier) and Unix-style file path syntax. More complex expressions can be constructed by specifying an axis other than the default 'child' axis, a node test other than a simple name, or predicates, which can be written in square brackets after any step. For example, the expression
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.
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.
XPath 3.1 [12] is an expression language that allows the processing of values conforming to the XDM [13] data model. The version 3.1 of XPath supports JSON as well as XML. jq is like sed for JSON data – it can be used to slice and filter and map and transform structured data.
XPath is an example of a path expression language. In concurrency control, path expressions are a mechanism for expressing permitted sequences of execution. For example, a path expression like "{read}, write" might specify that either multiple simultaneous executions of read or a single execution of write but not both are allowed at any point ...
Here, the list [0..] represents , x^2>3 represents the predicate, and 2*x represents the output expression.. List comprehensions give results in a defined order (unlike the members of sets); and list comprehensions may generate the members of a list in order, rather than produce the entirety of the list thus allowing, for example, the previous Haskell definition of the members of an infinite list.
By contrast, XSLT is a two-language system in which XPath expressions can be nested in XSLT instructions but not vice versa. XSLT is currently stronger than XQuery for applications that involve making small changes to a document (for example, deleting all the NOTE elements).
XPath (or XPath 1.0): an expression language for addressing portions of an XML document; XPath 2.0: a language for addressing portions of XML documents, successor of XPath 1.0; XPointer: a system for addressing components of XML based internet media; XProc : a W3C standard language to describe XML Pipeline