XPath Expressions

What is XPath ?

The power behind the power searches functionality is an excellent open source XML Native Database program called eXist.

XML Signature recommends a standard means for specifying information content to be digitally signed and for representing the resulting digital signatures in XML.

One of the themes I heard consistently at YAPC was that every XML hacker who learned XPath said their life had changed. I played a little with XPath last night while writing the XML chapter for Cookbook 2ed, and I have to say--they're right. XPath is incredible.

XPath (XML Path Language) is a set of rules for addressing parts of an XML document. Using XPath, it is possible to address any point in an XML document without the need for embedding anchors and so on in the document.

Nonstandard XPath functions are supported in FormsPlayer through COM methods. An XML file maps namespace URIs to COM ProgIds to give access to these methods. [PDF]

The XML Recommendation [XML] specifies the syntax of a class of objects called XML documents. The Namespaces in XML Recommendation [XML-NS] specifies additional syntax and semantics for XML documents.

In general, an XPath expression specifies a pattern that selects a set of XML nodes. XSLT templates then use those patterns when applying transformations. (XPointer, on the other hand, adds mechanisms for defining a point or a range, so that XPath expressions can be used for addressing.)

Uses an XPath language expression to search an XML document that is represented as a string variable.

Current node in each example shown in purple (in the tree) and large (in the XML). Nodes are always processed in document order. Note, however, that for the ancestor, ancestor-or-self, parent, preceding, and preceding-sibling axes, node selection order with "[1], [2], etc." goes "backward" or "upward," i.e. toward the root node.

The current implementation gets its inspiration from XPATH, but by no means it is a complete, or even a subset, implementation of the standard. Since it is built on top of the SAX interface, it uses a ``stream" paradigm which is completely alien to the XPATH specification.

SRW can be used to retrieve any sort of XML records, and is not limited by size or complexity in any way. Records in schemas such as TEI, EAD, SVG, X3D or OpenOffice's schema can be extremely long and complex

All XML Path Language (XPath) expressions occur within a particular context, that is, a single node against which the expression operates.

XPath (XML Path language) is typically the means for referring to and retrieving information from an XML document.

Overview of XSLT and XPath

SXPath is a query language for SXML. It treats a location path as a composite query over an XPath tree or its branch. A single step is a combination of a projection, selection or a transitive closure. Multiple steps are combined via join and union operations.

You can use XQuery and XPath to retrieve specific pieces of XML as you might retrieve data from a database. XQuery and XPath provide a syntax for specifying which elements and attributes you're interested in.

At bottom, XSLT is a language that lets you specify what sorts of things to do when a particular element is encountered. But to write a program for different parts of an XML data structure, you need to be able to specify the part of the structure you are talking about at any given time.

Having data in an XML document is one thing. But what if you want to query that data to see if a specific element exists? That's a job for XPath, the easy way to address specific parts of an XML document and find exactly what you're looking for.