THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

XPath: Location paths

XPath is a declarative language for:

addressing (used in XLink/XPointer and in XSLT)
pattern matching (used in XSLT and in XQuery)

The central construct is the location path, which is a sequence of location steps separated by /, e.g.:

child::section[position()<6] / descendant::cite / attribute::href

selects all href attributes in cite elements in the first 5 sections of an article document.

a location step is evaluated wrt. some context resulting in a set of nodes
a location path is evaluated compositionally, left-to-right, starting with some initial context
- location paths resemble operating system directory paths
- each node resulting from evaluation of one step is used as context for evaluation of the next, and the results are unioned together

A context consists of:

a context node
a context position and size (two integers)
variable bindings, a function library, and a set of namespace declarations

Initial context: defined externally (e.g. by XPointer, XSLT, or XQuery).
Location paths can be prefixed with / to use the document root as initial context node!

Note: in the XPath data model, the XML document tree has a special root node above the root element.

There is a strong analogy to directory paths (in UNIX). As an example, the directory path /*/d/*.txt selects a set of files, and the location path /*/d/*[@ext="txt"] select a set of XML elements.