Evaluation of the final step produces the final result, which is the result of the XQuery. These evaluations produce a new set of items, called the result, which then becomes the focus that is passed to the next step. The step is evaluated for each item in the focus. A step is evaluated with a set of input items (nodes and atomic values), sometimes called the focus. This algorithm is evaluated by evaluating each step moving from left to right through the sequence. Think of a path expression as an algorithm for traversing an XML tree to find and collect items of interest. Although path expressions are used for traversing XML trees, not file systems, in QtXmlPatterms we can model a file system to look like an XML tree, so in QtXmlPatterns we can use XQuery to traverse a file system. It is a sequence of one or more steps separated by slash '/' or double slash '//'. In XQuery, we write these iterative and recursive algorithms with path expressions.Ī path expression looks somewhat like a typical file pathname for locating a file in a hierarchical file system. In C++ and Java, we write nested for loops and recursive functions to traverse XML trees in search of elements of interest. Using Path Expressions To Match And Select Items
It creates a new element in the output and sets its id attribute to be the id attribute from an element in the other.html file. This XQuery has a document expression embedded in a node expression: But constructing new elements in an XQuery is often necessary.Īn XQuery expression can also be enclosed in curly braces and embedded in another XQuery expression. It just creates an empty element in the output. In fact, this XQuery doesn't actually query anything. This element is an XQuery expression that forms a complete XQuery. The simplest XQuery expression is an XML element constructor: Where Java and C++ are statement-based languages, the XQuery language is expression-based. XQuery is a language for querying XML data or non-XML data that can be modeled as XML.
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