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</h3>
<a name="wp64468"> </a><p class="pBody">
This section ends with an overview of the XPath functions. You can use XPath functions to select a collection of nodes in the same way that you would use an an element specification like those you have already seen. Other functions return a string, a number, or a boolean value. For example, the expression <code class="cCode">/PROJECT/text()</code> gets the string-value of <code class="cCode">PROJECT</code> nodes. 
</p>
<a name="wp64469"> </a><p class="pBody">
Many functions depend on the current context. In the example above, the <span style="font-style: italic">context</span> for each invocation of the <code class="cCode">text()</code> function is the <code class="cCode">PROJECT</code> node that is currently selected. 
</p>
<a name="wp64470"> </a><p class="pBody">
There are many XPath functions--too many to describe in detail here. This section provides a quick listing that shows the available XPath functions, along with a summary of what they do. 
</p>
<hr>
<a name="wp64471"> </a><p class="pNote">
Note: Skim the list of functions to get an idea of what's there. For more information, see Section 4 of the<a  href="http://www.w3.org/TR/xpath" target="_blank"> XPath Specification</a>.
</p>
<hr><a name="wp64472"> </a><h4 class="pHeading3">
Node-set functions
</h4>
<a name="wp64473"> </a><p class="pBody">
Many XPath expressions select a set of nodes. In essence, they return a <span style="font-style: italic">node-set</span>. One function does that, too.
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp64474"> </a><div class="pSmartList1"><li><code class="cCode">id(...)</code>--returns the node with the specified id.</li></div>
</ul></div>
<a name="wp64475"> </a><p class="pBody">
(Elements only have an ID when the document has a DTD, which specifies which attribute has the <code class="cCode">ID</code> type.)
</p>
<a name="wp64476"> </a><h4 class="pHeading3">
Positional functions
</h4>
<a name="wp64477"> </a><p class="pBody">
These functions return positionally-based numeric values. 
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp64478"> </a><div class="pSmartList1"><li><code class="cCode">last()</code>--returns the index of the last element. </li></div>
<a name="wp76601"> </a><p class="pBodyRelative">
For example: <code class="cCode">/HEAD[last()]</code> selects the last <code class="cCode">HEAD</code> element.
</p>
<a name="wp64479"> </a><div class="pSmartList1"><li><code class="cCode">position()</code>--returns the index position. </li></div>
<a name="wp76605"> </a><p class="pBodyRelative">
For example: <code class="cCode">/HEAD[position() &lt;= 5]</code> selects the first five <code class="cCode">HEAD</code> elements
</p>
<a name="wp64480"> </a><div class="pSmartList1"><li><code class="cCode">count(...)</code>--returns the count of elements. </li></div>
<a name="wp76609"> </a><p class="pBodyRelative">
For example: <code class="cCode">/HEAD[count(HEAD)=0]</code> selects all <code class="cCode">HEAD</code> elements that have no subheads.
</p>
</ul></div>
<a name="wp64481"> </a><h4 class="pHeading3">
String functions
</h4>
<a name="wp64482"> </a><p class="pBody">
These functions operate on or return strings.
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp64483"> </a><div class="pSmartList1"><li><code class="cCode">concat(</code><code class="cVariable">string</code><code class="cCode">, </code><code class="cVariable">string</code><code class="cCode">, ...)</code>--concatenates the string values</li></div>
<a name="wp64484"> </a><div class="pSmartList1"><li><code class="cCode">starts-with(</code><code class="cVariable">string1</code><code class="cCode">, </code><code class="cVariable">string2</code><code class="cCode">)</code>--returns true if <code class="cVariable">string1</code> starts with <code class="cVariable">string2</code></li></div>
<a name="wp64485"> </a><div class="pSmartList1"><li><code class="cCode">contains(</code><code class="cVariable">string1</code><code class="cCode">, </code><code class="cVariable">string2</code><code class="cCode">)</code>--returns true if <code class="cVariable">string1</code> contains <code class="cVariable">string2</code> </li></div>
<a name="wp64486"> </a><div class="pSmartList1"><li><code class="cCode">substring-before(</code><code class="cVariable">string1</code><code class="cCode">, </code><code class="cVariable">string2</code><code class="cCode">)</code>--returns the start of <code class="cVariable">string1</code> before <code class="cVariable">string2</code> occurs in it</li></div>
<a name="wp64487"> </a><div class="pSmartList1"><li><code class="cCode">substring-after(</code><code class="cVariable">string1</code><code class="cCode">, </code><code class="cVariable">string2</code><code class="cCode">)</code>--returns the remainder of <code class="cVariable">string1</code> after <code class="cVariable">string2</code> occurs in it</li></div>
<a name="wp64488"> </a><div class="pSmartList1"><li><code class="cCode">substring(</code><code class="cVariable">string</code><code class="cCode">, </code><code class="cVariable">idx</code><code class="cCode">)</code>--returns the substring from the index position to the end, where the index of the first char = 1</li></div>
<a name="wp64489"> </a><div class="pSmartList1"><li><code class="cCode">substring(</code><code class="cVariable">string</code><code class="cCode">, </code><code class="cVariable">idx</code><code class="cCode">, </code><code class="cVariable">len</code><code class="cCode">)</code>--returns the substring from the index position, of the specified length</li></div>
<a name="wp64490"> </a><div class="pSmartList1"><li><code class="cCode">string-length()</code>--returns the size of the context-node's string-value</li></div>
<a name="wp77077"> </a><p class="pBodyRelative">
The <span style="font-style: italic">context node</span> is the currently selected node -- the node that was selected by an XPath expression in which a function like <code class="cCode">string-length()</code> is applied.
</p>
<a name="wp64491"> </a><div class="pSmartList1"><li><code class="cCode">string-length(</code><code class="cVariable">string</code><code class="cCode">)</code>--returns the size of the specified string </li></div>
<a name="wp64492"> </a><div class="pSmartList1"><li><code class="cCode">normalize-space()</code>--returns the normalized string-value of the current node (no leading or trailing whitespace, and sequences of whitespace characters converted to a single space)</li></div>
<a name="wp64493"> </a><div class="pSmartList1"><li><code class="cCode">normalize-space(</code><code class="cVariable">string</code><code class="cCode">)</code>--returns the normalized string-value of the specified string</li></div>
<a name="wp64494"> </a><div class="pSmartList1"><li><code class="cCode">translate(</code><code class="cVariable">string1</code><code class="cCode">, </code><code class="cVariable">string2</code><code class="cCode">, </code><code class="cVariable">string3</code><code class="cCode">)</code>--converts <code class="cVariable">string1</code>, replacing occurrences of characters in <code class="cVariable">string2</code> with the corresponding character from <code class="cVariable">string3</code></li></div>
</ul></div>
<hr>
<a name="wp64495"> </a><p class="pNote">
Note: XPath defines 3 ways to get the text of an element: <code class="cCode">text()</code>, <code class="cCode">string(object)</code>, and the string-value implied by an element name in an expression like this: <code class="cCode">/PROJECT[PERSON=&quot;Fred&quot;]</code>.
</p>
<hr><a name="wp64496"> </a><h4 class="pHeading3">
Boolean functions
</h4>
<a name="wp64497"> </a><p class="pBody">
These functions operate on or return boolean values:
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp64498"> </a><div class="pSmartList1"><li><code class="cCode">not(...)</code>--negates the specified boolean value</li></div>
<a name="wp64499"> </a><div class="pSmartList1"><li><code class="cCode">true()</code>--returns true </li></div>
<a name="wp64500"> </a><div class="pSmartList1"><li><code class="cCode">false()</code>--returns false </li></div>
<a name="wp64501"> </a><div class="pSmartList1"><li><code class="cCode">lang(</code><code class="cVariable">string</code><code class="cCode">)</code>--returns true if the language of the context node (specified by <code class="cCode">xml:Lang</code> attributes) is the same as (or a sublanguage of) the specified language. For example: <code class="cCode">Lang(&quot;en&quot;)</code> is true for <code class="cCode">&lt;PARA_xml:Lang=&quot;en&quot;&gt;...&lt;/PARA&gt;</code> </li></div>
</ul></div>
<a name="wp64502"> </a><h4 class="pHeading3">
Numeric functions
</h4>
<a name="wp64503"> </a><p class="pBody">
These functions operate on or return numeric values. 
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp64504"> </a><div class="pSmartList1"><li><code class="cCode">sum(...)</code>--returns the sum of the numeric value of each node in the specified node-set</li></div>
<a name="wp64505"> </a><div class="pSmartList1"><li><code class="cCode">floor(</code><code class="cVariable">N</code><code class="cCode">)</code>--returns the largest integer that is not greater than <code class="cVariable">N</code></li></div>
<a name="wp64506"> </a><div class="pSmartList1"><li><code class="cCode">ceiling(</code><code class="cVariable">N</code><code class="cCode">)</code>--returns the smallest integer that is greater than <code class="cVariable">N</code></li></div>
<a name="wp64507"> </a><div class="pSmartList1"><li><code class="cCode">round(</code><code class="cVariable">N</code><code class="cCode">)</code>--returns the integer that is closest to <code class="cVariable">N</code></li></div>
</ul></div>
<a name="wp64508"> </a><h4 class="pHeading3">
Conversion functions
</h4>
<a name="wp64509"> </a><p class="pBody">
These functions convert one data type to another.
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp64510"> </a><div class="pSmartList1"><li><code class="cCode">string(...)</code>--returns the string value of a number, boolean, or node-set</li></div>
<a name="wp64511"> </a><div class="pSmartList1"><li><code class="cCode">boolean(...)</code>--returns a boolean value for a number, string, or node-set (a non-zero number, a non-empty node-set, and a non-empty string are all true)</li></div>
<a name="wp64513"> </a><div class="pSmartList1"><li><code class="cCode">number(...)</code>--returns the numeric value of a boolean, string, or node-set (true is 1, false is 0, a string containing a number becomes that number, the string-value of a node-set is converted to a number)</li></div>
</ul></div>
<a name="wp64515"> </a><h4 class="pHeading3">
Namespace functions
</h4>
<a name="wp64516"> </a><p class="pBody">
These functions let you determine the namespace characteristics of a node. 
</p>
<div class="pSmartList1"><ul class="pSmartList1">
<a name="wp64517"> </a><div class="pSmartList1"><li><code class="cCode">local-name()</code>--returns the name of the current node, minus the namespace prefix</li></div>
<a name="wp64518"> </a><div class="pSmartList1"><li><code class="cCode">local-name(...)</code>--returns the name of the first node in the specified node set, minus the namespace prefix</li></div>
<a name="wp64519"> </a><div class="pSmartList1"><li><code class="cCode">namespace-uri()</code>--returns the namespace URI from the current node</li></div>
<a name="wp64520"> </a><div class="pSmartList1"><li><code class="cCode">namespace-uri(...)</code>--returns the namespace URI from the first node in the specified node set</li></div>
<a name="wp64521"> </a><div class="pSmartList1"><li><code class="cCode">name()</code>--returns the expanded name (URI plus local name) of the current node</li></div>
<a name="wp64522"> </a><div class="pSmartList1"><li><code class="cCode">name(...)</code>--returns the expanded name (URI plus local name) of the first node in the specified node set</li></div>
</ul></div>
<a name="wp64523"> </a><h3 class="pHeading2">
Summary
</h3>
<a name="wp64524"> </a><p class="pBody">
XPath operators, functions, wildcards, and node-addressing mechanisms can be combined in wide variety of ways. The introduction you've had so far should give you a good head start at specifying the pattern you need for any particular purpose. 
</p>
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