XML Introduktion / XML og XSL(T) / XPath introduktion

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XPath

XPath bruges til at angive en position i et XML dokument (lidt som vi kan angive en mappe eller en fil på vores harddisk). XPath er meget central i arbejdet med XSL, men nok lidt for omfattende til at vi kan give det en nærmere behandling i denne sammenhæng. Jeg vil derfor tillade mig at henvise til nedenstående tekst og behandlingen på XSL kurset.

In order to retrieve arbitrary nodes, you can use the match attribute of the <xsl:template> element to determine the current context. This attribute takes an XPath expression to determine to what set of elements from the XML document the current template will apply.

So what exactly is an XPath expression? XPath is a huge specification in its own right. In this course, only the basics of XPath can be covered. The table below provides the essentials of this syntax - its core operators and special characters:

XPath Basic Syntax	Definition
/	The Child operator. It selects the immediate children of the collection to the left of this character. If no such collection exists, then the children of the root are selected.
//	A Recursive selector. It searches for the specified element at any depth in the current context.
.	The current context in the XML document.
..	The parent of the current node.
:	Namespace separator, similar to its use in <xsl:template> for instance.
*	A wildcard character. It will select all elements.
@	An attribute. It serves as a prefix before the attribute name. If no name follows it, then it acts as an attribute wildcard.
()	Groups operations to establish precedence.
+	Addition.
-	Subtraction.
div	Division.
*	Multiplication.
mod	The remainder from a division operation that truncates the result.
[]	Applies a filter pattern.

Some of this syntax should be familiar to you from other contexts. The mathematics operators for instance are standard, though it is interesting to note that div is used for division, since / has an alternate meaning.