xdocs/sources/xsltc/xsltc_runtime.xml - xalan-j - Git at Google

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   <s1 title="XSLTC runtime environment">
   <ul>
     <li><link anchor="overview">Runtime overview</link></li>
     <li><link anchor="translet">The compiled translet</link></li>
     <li><link anchor="types">External/internal type mapping</link></li>
     <li><link anchor="mainloop">Main program loop</link></li>

   </ul>
   <anchor name="overview"/>
   <s2 title="Runtime overview">
     <p>The actual transformation of the input XML document is initiated by
     one of these classes:</p>

     <ul>
       <li>
         <code>com.sun.xslt.runtime.DefaultRun</code> (runs in a terminal)
       </li>
       <li>
         <code>com.sun.xslt.demo.applet.TransformApplet</code> (runs in an applet)
       </li>
       <li>
         <code>com.sun.xslt.demo.servlet.Translate</code> (runs in a servlet)
       </li>
     </ul>

     <p>Any one of these classes will have to go through the folloing steps in
     order to initiate a transformation:</p>

     <ul>
       <li>
         Instanciate the translet object. The name of the translet (ie. class)
         to use is passed to us as a string. We use this string as a parameter
         to the static method <code>Class.forName(String name)</code> to get a
         reference to a translet object.
       </li>
       <li>
         Instanciate a <code>com.sun.xsl.parser.Parser</code> object to parse the
         input XML file, and instanciate a DOM (we have our own DOM
         implementation especially designed for XSLTC) where we store the
         input document.
       </li>
       <li>
         Pass any parameters to the translet (currently only possible when
         running the transformation in a terminal using DefaultRun)
       </li>
       <li>
         Instanciate a handler for the result document. This handler must be
         extend the <code>TransletOutputHandler</code> class.
       </li>
       <li>
         Invoke the <code>transform()</code> method on the translet, passing the
         instanciated DOM and the output handler as parameters.
       </li>
     </ul>

     </s2><anchor name="translet"/>
     <s2 title="The compiled translet">

     <p>A translet is always a subclass of <code>AbstractTranslet</code>. As well
     as having access to the public/protected methods in this class, the
     translet is compiled with these methods:</p>

     <p><code>public void transform(DOM, NodeIterator, TransletOutputHandler);</code></p>

     <p>This method is passed a <code>DOMImpl</code> object. Depending on whether
     the stylesheet had any calls to the <code>document()</code> function this
     method will either generate a <code>DOMAdapter</code> object (when only one
     XML document is used as input) or a <code>MultiDOM</code> object (when there
     are more than one XML input documents). This DOM object is passed on to
     the <code>topLevel()</code> method.</p>

     <p>When the <code>topLevel()</code> method returns we initiate the output
     document by calling <code>startDocument()</code> on the supplied output
     handler object. We then call <code>applyTemplates()</code> to get the actual
     output contents, before we close the output document by calling
     <code>endDocument()</code> on the output handler.</p>

     <p><code>public void topLevel(DOM, NodeIterator, TransletOutputHandler);</code></p>

     <p>This method handles all of these top-level elements:</p>
     <ul>
       <li><code>&lt;xsl:output&gt;</code></li>
       <li><code>&lt;xsl:decimal-format&gt;</code></li>
       <li><code>&lt;xsl:key&gt;</code></li>
       <li><code>&lt;xsl:param&gt;</code> (for global parameters)</li>
       <li><code>&lt;xsl:variable&gt;</code> (for global variables)</li>
     </ul>

     <p><code>public void applyTemplates(DOM, NodeIterator, TransletOutputHandler);</code></p>

     <p>This is the method that produces the actual output. Its central element
     is a big <code>switch()</code> statement that is used to choose the available
     templates for the various node in the input document. See the chapter
     <link anchor="mainloop">Main Program Loop</link> for details on this method.</p>

     <p><code>public void &lt;init&gt; ();</code></p>
     <anchor name="namesarray"/>
     <p>The translet's constructor initializes a table
     of all the elements we want to search for in the XML input document.
     This table is called the <code>namesArray</code> and it is passed to the DOM
     holding the input XML document.</p>

     <p>The constructor also initializes any <code>DecimalFormatSymbol</code>
     objects that are used to format numbers before passing them to the
     output handler.</p>

     <p><code>public boolean stripSpace(int nodeType);</code></p>

     <p>This method is only present if any <code>&lt;xsl:strip-space&gt;</code> or
     <code>&lt;xsl:preserve-space&gt;</code> elements are present in the stylesheet.
     If that is the case, the translet implements the
     <code>StripWhitespaceFilter</code> interface by containing this method.</p>

     </s2><anchor name="types"/>
     <s2 title="External/internal type mapping">

     <anchor name="external-types"/>

     <p>This is the very core of XSL transformations: <em>Read carefully!!!</em></p>

     <p>Every node in the input XML document(s) is assigned a type by the
     DOM builder class. This type is an integer value which represents the
     element, so that for instance all <code>&lt;bob&gt;</code> elements in the
     input document will be given type <ref>7</ref> and can be referred to by using
     that integer. These types can be used for lookups in the
     <link anchor="namesarray">namesArray</link> table to get the actual
     element name (in this case "bob"). These types are referred to as
     <em>external types</em> or <em>DOM types</em>, as they are types known only
     to the DOM and the DOM builder.</p>

     <anchor name="internal-types"/>

     <p>Similarly the translet assignes types to all element and attribute names
     that are referenced in the stylesheet. These types are referred to as
     <em>internal types</em> or <em>translet types</em>.</p>

     <p>It is not very probable that there will be a one-to-one mapping between
     internal and external types. There will most often be elements in the DOM
     (ie. the input document) that are not mentioned in the stylesheet, and
     there could be elements in the stylesheet that do not match any elements
     in the DOM. Here is an example:</p>

 <source>
       &lt;?xml version="1.0"?&gt;
       &lt;xsl:stylesheet version="1.0" xmlns:xsl="blahblahblah"&gt;

       &lt;xsl:template match="/"&gt;
         &lt;xsl:for-each select="//B"&gt;
           &lt;xsl:apply-templates select="." /&gt;
         &lt;/xsl:for-each&gt;
         &lt;xsl:for-each select="C"&gt;
           &lt;xsl:apply-templates select="." /&gt;
         &lt;/xsl:for-each&gt;
         &lt;xsl:for-each select="A/B"&gt;
           &lt;xsl:apply-templates select="." /&gt;
         &lt;/xsl:for-each&gt;
       &lt;/xsl:template&gt;

     &lt;/xsl:stylesheet&gt;
 </source>

     <p>In this stylesheet we are looking for elements <code>&lt;B&gt;</code>,
     <code>&lt;C&gt;</code> and <code>&lt;A&gt;</code>. For this example we can assume
     that these element types will be assigned the values 0, 1 and 2. Now, lets
     say we are transforming this XML document:</p>

 <source>
       &lt;?xml version="1.0"?&gt;

       &lt;A&gt;
         The crocodile cried:
         &lt;F&gt;foo&lt;/F&gt;
         &lt;B&gt;bar&lt;/B&gt;
         &lt;B&gt;baz&lt;/B&gt;
       &lt;/A&gt;
 </source>

     <p>This XML document has the elements <code>&lt;A&gt;</code>,
     <code>&lt;B&gt;</code> and <code>&lt;F&gt;</code>, which we assume are assigned the
     types 7, 8 and 9 respectively  (the numbers below that are assigned for
     specific element types, such as the root node, text nodes, etc.). This
     causes a mismatch between the type used for <code>&lt;B&gt;</code> in the
     translet and the type used for <code>&lt;B&gt;</code> in the DOM. Th
     DOMAdapter class (which mediates between the DOM and the translet) has been
     given two tables for convertint between the two types; <code>mapping</code> for
     mapping from internal to external types, and <code>reverseMapping</code> for
     the other way around.</p>

     <p>The translet contains a <code>String[]</code> array called
     <code>namesArray</code>. This array will contain all the element and attribute
     names that were referenced in the stylesheet. In our example, this array
     would contain these string (in this specific order): &quot;B&quot;,
     &quot;C&quot; and &quot;A&quot;. This array is passed as one of the
     parameters to the DOM adapter constructor (the other adapter is the DOM
     itself). The DOM adapter passes this table on to the DOM. The DOM has
     a hashtable that maps known element names to external types. The DOM goes
     through the <code>namesArray</code> from the DOM sequentially, looks up each
     name in the hashtable, and is then able to map the internal type to an
     external type. The result is then passed back to the DOM adapter.</p>

     <p>The reverse is done for external types. External types that are not
     interesting for the translet (such as the type for <code>&lt;F&gt;</code>
     elements in the example above) are mapped to a generic <code>"ELEMENT"</code>
     type 3, and are more or less ignored by the translet.</p>

     <p>It is important that we separate the DOM from the translet. In several
     cases we want the DOM as a structure completely independent from the
     translet - even though the DOM is a structure internal to XSLTC. One such
     case is when transformations are offered by a servlet as a web service.
     Any DOM that is built should potentially be stored in a cache and made
     available for simultaneous access by several translet/servlet couples.</p>

     <p><img src="runtime_type_mapping.gif" alt="runtime_type_mapping.gif"/></p>
     <p><ref>Figure 1: Two translets accessing a single dom using different type mappings</ref></p>

     </s2><anchor name="mainloop"/>
     <s2 title="Main program loop">

     <p>The main loop in the translet is found in the <code>applyTemplates()</code>
     method. This method goes through these steps:</p>

     <ul>
       <li>
         Get the next node from the node iterator
       </li>
       <li>
         Get the internal type of this node. The DOMAdapter object holds the
         internal/external type mapping table, and it will supply the translet
         with the internal type of the current node.
       </li>
       <li>
         Execute a switch statement on the internal node type. There will be
         one "case" label for each recognised node type - this includes the
         first 7 internal node types.
       </li>
     </ul>

     <p>The root node will have internal type 0 and will cause any initial
     literal elements to be output. Text nodes will have internal node type 1
     and will simply be dumped to the output handler. Unrecognized elements
     will have internal node type 3 and will be given the default treatment
     (a new iterator is created for the node's children, and this iterator
     is passed with a recursive call to <code>applyTemplates()</code>).
     Unrecognised attribute nodes (type 4) will be handled like text nodes.
     The <code>switch()</code> statement in <code>applyTemplates</code> will thereby
     look something like this:</p>

 <source>
         public void applyTemplates(DOM dom, NodeIterator,
                                    TransletOutputHandler handler) {

             // get nodes from iterator
             while ((node = iterator.next()) != END) {
                 // get internal node type
                 switch(DOM.getType(node)) {

                 case 0: // root
                     outputPreable(handler);
                     break;
                 case 1: // text
                     DOM.characters(node,handler);
                     break;
                 case 3: // unrecognised element
                     NodeIterator newIterator = DOM.getChildren(node);
                     applyTemplates(DOM,newIterator,handler);
                     break;
                 case 4: // unrecognised attribute
                     DOM.characters(node,handler);
                     break;
                 case 7: // elements of type &lt;B&gt;
                     someCompiledCode();
                     break;
                 case 8: // elements of type &lt;C&gt;
                     otherCompiledCode();
                     break;
                 default:
                     break;
                 }
             }
         }
 </source>

     <p>Each recognised element will have its own piece of compiled code.</p>

     <p>Note that each "case" will not lead directly to a single template.
     There may be several templates that match node type 7
     (say <code>&lt;B&gt;</code>). In the sample stylesheet in the previous chapter
     we have to templates that would match a node <code>&lt;B&gt;</code>. We have
     one <code>match="//B"</code> (match just any <code>&lt;B&gt;</code> element) and
     one <code>match="A/B"</code> (match a <code>&lt;B&gt;</code> element that is a
     child of a <code>&lt;A&gt;</code> element). In this case we would have to
     compile code that first gets the type of the current node's parent, and
     then compared this type with the type for <code>&lt;A&gt;</code>. If there was
     no match we will have executed the first <code>&lt;xsl:for-each&gt;</code>
     element, but if there was a match we will have executed the last one.
     Consequentally, the compiler will generate the following code:</p>

 <source>
         switch(DOM.getType(node)) {
           :
           :
         case 7: // elements of type &lt;B&gt;
             int parent = DOM.getParent(node);
             if (DOM.getType(parent) == 9) // type 9 = elements &lt;A&gt;
                 someCompiledCode();
             else
                 evenOtherCompiledCode();
             break;
           :
           :
         }
 </source>

     <p>We could do the same for namespaces, that is, assign a numeric value
     to every namespace that is references in the stylesheet, and use an
     <code>"if"</code> statement for each namespace that needs to be checked for
     each type. Lets say we had a stylesheet like this:</p>

 <source>
       &lt;?xml version="1.0"?&gt;
       &lt;xsl:stylesheet version="1.0" xmlns:xsl="blahblahblah"&gt;

       &lt;xsl:template match="/"
           xmlns:foo="http://foo.com/spec"
           xmlns:bar="http://bar.net/ref"&gt;
         &lt;xsl:for-each select="foo:A"&gt;
           &lt;xsl:apply-templates select="." /&gt;
         &lt;/xsl:for-each&gt;
         &lt;xsl:for-each select="bar:A"&gt;
           &lt;xsl:apply-templates select="." /&gt;
         &lt;/xsl:for-each&gt;
       &lt;/xsl:template&gt;

     &lt;/xsl:stylesheet&gt;
 </source>

     <p>And a stylesheet like this:</p>

 <source>
       &lt;?xml version="1.0"?&gt;

       &lt;DOC
           xmlns:foo="http://foo.com/spec"
           xmlns:bar="http://bar.net/ref"&gt;
         &lt;foo:A&gt;In foo namespace&lt;/foo:A&gt;
         &lt;bar:A&gt;In bar namespace&lt;/bar:A&gt;
       &lt;/DOC&gt;
 </source>

     <p>We could still keep the same type for all <code>&lt;A&gt;</code> elements
     regardless of what namespace they are in, and use the same <code>"if"</code>
     structure within the <code>switch()</code> statement above. The other option
     is to assign different types to <code>&lt;foo:A&gt;</code> and
     <code>&lt;bar:A&gt;</code> elements.</p>

   </s2>
 </s1>
	<?xml version="1.0" standalone="no"?>
	<!DOCTYPE s1 SYSTEM "../../style/dtd/document.dtd">
	<!--
	* The Apache Software License, Version 1.1
	*
	*
	* Copyright (c) 2001 The Apache Software Foundation. All rights
	* reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	*
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	*
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in
	* the documentation and/or other materials provided with the
	* distribution.
	*
	* 3. The end-user documentation included with the redistribution,
	* if any, must include the following acknowledgment:
	* "This product includes software developed by the
	* Apache Software Foundation (http://www.apache.org/)."
	* Alternately, this acknowledgment may appear in the software itself,
	* if and wherever such third-party acknowledgments normally appear.
	*
	* 4. The names "Xalan" and "Apache Software Foundation" must
	* not be used to endorse or promote products derived from this
	* software without prior written permission. For written
	* permission, please contact apache@apache.org.
	*
	* 5. Products derived from this software may not be called "Apache",
	* nor may "Apache" appear in their name, without prior written
	* permission of the Apache Software Foundation.
	*
	* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
	* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
	* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
	* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
	* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
	* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	* SUCH DAMAGE.
	* ====================================================================
	*
	* This software consists of voluntary contributions made by many
	* individuals on behalf of the Apache Software Foundation and was
	* originally based on software copyright (c) 2001, Sun
	* Microsystems., http://www.sun.com. For more
	* information on the Apache Software Foundation, please see
	* <http://www.apache.org/>.
	-->
	<s1 title="XSLTC runtime environment">
	<ul>
	<li><link anchor="overview">Runtime overview</link></li>
	<li><link anchor="translet">The compiled translet</link></li>
	<li><link anchor="types">External/internal type mapping</link></li>
	<li><link anchor="mainloop">Main program loop</link></li>

	</ul>
	<anchor name="overview"/>
	<s2 title="Runtime overview">
	<p>The actual transformation of the input XML document is initiated by
	one of these classes:</p>

	<ul>
	<li>
	<code>com.sun.xslt.runtime.DefaultRun</code> (runs in a terminal)
	</li>
	<li>
	<code>com.sun.xslt.demo.applet.TransformApplet</code> (runs in an applet)
	</li>
	<li>
	<code>com.sun.xslt.demo.servlet.Translate</code> (runs in a servlet)
	</li>
	</ul>

	<p>Any one of these classes will have to go through the folloing steps in
	order to initiate a transformation:</p>

	<ul>
	<li>
	Instanciate the translet object. The name of the translet (ie. class)
	to use is passed to us as a string. We use this string as a parameter
	to the static method <code>Class.forName(String name)</code> to get a
	reference to a translet object.
	</li>
	<li>
	Instanciate a <code>com.sun.xsl.parser.Parser</code> object to parse the
	input XML file, and instanciate a DOM (we have our own DOM
	implementation especially designed for XSLTC) where we store the
	input document.
	</li>
	<li>
	Pass any parameters to the translet (currently only possible when
	running the transformation in a terminal using DefaultRun)
	</li>
	<li>
	Instanciate a handler for the result document. This handler must be
	extend the <code>TransletOutputHandler</code> class.
	</li>
	<li>
	Invoke the <code>transform()</code> method on the translet, passing the
	instanciated DOM and the output handler as parameters.
	</li>
	</ul>

	</s2><anchor name="translet"/>
	<s2 title="The compiled translet">

	<p>A translet is always a subclass of <code>AbstractTranslet</code>. As well
	as having access to the public/protected methods in this class, the
	translet is compiled with these methods:</p>

	<p><code>public void transform(DOM, NodeIterator, TransletOutputHandler);</code></p>

	<p>This method is passed a <code>DOMImpl</code> object. Depending on whether
	the stylesheet had any calls to the <code>document()</code> function this
	method will either generate a <code>DOMAdapter</code> object (when only one
	XML document is used as input) or a <code>MultiDOM</code> object (when there
	are more than one XML input documents). This DOM object is passed on to
	the <code>topLevel()</code> method.</p>

	<p>When the <code>topLevel()</code> method returns we initiate the output
	document by calling <code>startDocument()</code> on the supplied output
	handler object. We then call <code>applyTemplates()</code> to get the actual
	output contents, before we close the output document by calling
	<code>endDocument()</code> on the output handler.</p>

	<p><code>public void topLevel(DOM, NodeIterator, TransletOutputHandler);</code></p>

	<p>This method handles all of these top-level elements:</p>
	<ul>
	<li><code><xsl:output></code></li>
	<li><code><xsl:decimal-format></code></li>
	<li><code><xsl:key></code></li>
	<li><code><xsl:param></code> (for global parameters)</li>
	<li><code><xsl:variable></code> (for global variables)</li>
	</ul>

	<p><code>public void applyTemplates(DOM, NodeIterator, TransletOutputHandler);</code></p>

	<p>This is the method that produces the actual output. Its central element
	is a big <code>switch()</code> statement that is used to choose the available
	templates for the various node in the input document. See the chapter
	<link anchor="mainloop">Main Program Loop</link> for details on this method.</p>

	<p><code>public void <init> ();</code></p>
	<anchor name="namesarray"/>
	<p>The translet's constructor initializes a table
	of all the elements we want to search for in the XML input document.
	This table is called the <code>namesArray</code> and it is passed to the DOM
	holding the input XML document.</p>

	<p>The constructor also initializes any <code>DecimalFormatSymbol</code>
	objects that are used to format numbers before passing them to the
	output handler.</p>

	<p><code>public boolean stripSpace(int nodeType);</code></p>

	<p>This method is only present if any <code><xsl:strip-space></code> or
	<code><xsl:preserve-space></code> elements are present in the stylesheet.
	If that is the case, the translet implements the
	<code>StripWhitespaceFilter</code> interface by containing this method.</p>

	</s2><anchor name="types"/>
	<s2 title="External/internal type mapping">

	<anchor name="external-types"/>

	<p>This is the very core of XSL transformations: <em>Read carefully!!!</em></p>

	<p>Every node in the input XML document(s) is assigned a type by the
	DOM builder class. This type is an integer value which represents the
	element, so that for instance all <code><bob></code> elements in the
	input document will be given type <ref>7</ref> and can be referred to by using
	that integer. These types can be used for lookups in the
	<link anchor="namesarray">namesArray</link> table to get the actual
	element name (in this case "bob"). These types are referred to as
	<em>external types</em> or <em>DOM types</em>, as they are types known only
	to the DOM and the DOM builder.</p>

	<anchor name="internal-types"/>

	<p>Similarly the translet assignes types to all element and attribute names
	that are referenced in the stylesheet. These types are referred to as
	<em>internal types</em> or <em>translet types</em>.</p>

	<p>It is not very probable that there will be a one-to-one mapping between
	internal and external types. There will most often be elements in the DOM
	(ie. the input document) that are not mentioned in the stylesheet, and
	there could be elements in the stylesheet that do not match any elements
	in the DOM. Here is an example:</p>

	<source>
	<?xml version="1.0"?>
	<xsl:stylesheet version="1.0" xmlns:xsl="blahblahblah">

	<xsl:template match="/">
	<xsl:for-each select="//B">
	<xsl:apply-templates select="." />
	</xsl:for-each>
	<xsl:for-each select="C">
	<xsl:apply-templates select="." />
	</xsl:for-each>
	<xsl:for-each select="A/B">
	<xsl:apply-templates select="." />
	</xsl:for-each>
	</xsl:template>

	</xsl:stylesheet>
	</source>

	<p>In this stylesheet we are looking for elements <code><B></code>,
	<code><C></code> and <code><A></code>. For this example we can assume
	that these element types will be assigned the values 0, 1 and 2. Now, lets
	say we are transforming this XML document:</p>

	<source>
	<?xml version="1.0"?>

	<A>
	The crocodile cried:
	<F>foo</F>
	<B>bar</B>
	<B>baz</B>
	</A>
	</source>

	<p>This XML document has the elements <code><A></code>,
	<code><B></code> and <code><F></code>, which we assume are assigned the
	types 7, 8 and 9 respectively (the numbers below that are assigned for
	specific element types, such as the root node, text nodes, etc.). This
	causes a mismatch between the type used for <code><B></code> in the
	translet and the type used for <code><B></code> in the DOM. Th
	DOMAdapter class (which mediates between the DOM and the translet) has been
	given two tables for convertint between the two types; <code>mapping</code> for
	mapping from internal to external types, and <code>reverseMapping</code> for
	the other way around.</p>

	<p>The translet contains a <code>String[]</code> array called
	<code>namesArray</code>. This array will contain all the element and attribute
	names that were referenced in the stylesheet. In our example, this array
	would contain these string (in this specific order): "B",
	"C" and "A". This array is passed as one of the
	parameters to the DOM adapter constructor (the other adapter is the DOM
	itself). The DOM adapter passes this table on to the DOM. The DOM has
	a hashtable that maps known element names to external types. The DOM goes
	through the <code>namesArray</code> from the DOM sequentially, looks up each
	name in the hashtable, and is then able to map the internal type to an
	external type. The result is then passed back to the DOM adapter.</p>

	<p>The reverse is done for external types. External types that are not
	interesting for the translet (such as the type for <code><F></code>
	elements in the example above) are mapped to a generic <code>"ELEMENT"</code>
	type 3, and are more or less ignored by the translet.</p>

	<p>It is important that we separate the DOM from the translet. In several
	cases we want the DOM as a structure completely independent from the
	translet - even though the DOM is a structure internal to XSLTC. One such
	case is when transformations are offered by a servlet as a web service.
	Any DOM that is built should potentially be stored in a cache and made
	available for simultaneous access by several translet/servlet couples.</p>

	<p><img src="runtime_type_mapping.gif" alt="runtime_type_mapping.gif"/></p>
	<p><ref>Figure 1: Two translets accessing a single dom using different type mappings</ref></p>

	</s2><anchor name="mainloop"/>
	<s2 title="Main program loop">

	<p>The main loop in the translet is found in the <code>applyTemplates()</code>
	method. This method goes through these steps:</p>

	<ul>
	<li>
	Get the next node from the node iterator
	</li>
	<li>
	Get the internal type of this node. The DOMAdapter object holds the
	internal/external type mapping table, and it will supply the translet
	with the internal type of the current node.
	</li>
	<li>
	Execute a switch statement on the internal node type. There will be
	one "case" label for each recognised node type - this includes the
	first 7 internal node types.
	</li>
	</ul>

	<p>The root node will have internal type 0 and will cause any initial
	literal elements to be output. Text nodes will have internal node type 1
	and will simply be dumped to the output handler. Unrecognized elements
	will have internal node type 3 and will be given the default treatment
	(a new iterator is created for the node's children, and this iterator
	is passed with a recursive call to <code>applyTemplates()</code>).
	Unrecognised attribute nodes (type 4) will be handled like text nodes.
	The <code>switch()</code> statement in <code>applyTemplates</code> will thereby
	look something like this:</p>

	<source>
	public void applyTemplates(DOM dom, NodeIterator,
	TransletOutputHandler handler) {

	// get nodes from iterator
	while ((node = iterator.next()) != END) {
	// get internal node type
	switch(DOM.getType(node)) {

	case 0: // root
	outputPreable(handler);
	break;
	case 1: // text
	DOM.characters(node,handler);
	break;
	case 3: // unrecognised element
	NodeIterator newIterator = DOM.getChildren(node);
	applyTemplates(DOM,newIterator,handler);
	break;
	case 4: // unrecognised attribute
	DOM.characters(node,handler);
	break;
	case 7: // elements of type <B>
	someCompiledCode();
	break;
	case 8: // elements of type <C>
	otherCompiledCode();
	break;
	default:
	break;
	}
	}
	}
	</source>

	<p>Each recognised element will have its own piece of compiled code.</p>

	<p>Note that each "case" will not lead directly to a single template.
	There may be several templates that match node type 7
	(say <code><B></code>). In the sample stylesheet in the previous chapter
	we have to templates that would match a node <code><B></code>. We have
	one <code>match="//B"</code> (match just any <code><B></code> element) and
	one <code>match="A/B"</code> (match a <code><B></code> element that is a
	child of a <code><A></code> element). In this case we would have to
	compile code that first gets the type of the current node's parent, and
	then compared this type with the type for <code><A></code>. If there was
	no match we will have executed the first <code><xsl:for-each></code>
	element, but if there was a match we will have executed the last one.
	Consequentally, the compiler will generate the following code:</p>

	<source>
	switch(DOM.getType(node)) {
	:
	:
	case 7: // elements of type <B>
	int parent = DOM.getParent(node);
	if (DOM.getType(parent) == 9) // type 9 = elements <A>
	someCompiledCode();
	else
	evenOtherCompiledCode();
	break;
	:
	:
	}
	</source>

	<p>We could do the same for namespaces, that is, assign a numeric value
	to every namespace that is references in the stylesheet, and use an
	<code>"if"</code> statement for each namespace that needs to be checked for
	each type. Lets say we had a stylesheet like this:</p>

	<source>
	<?xml version="1.0"?>
	<xsl:stylesheet version="1.0" xmlns:xsl="blahblahblah">

	<xsl:template match="/"
	xmlns:foo="http://foo.com/spec"
	xmlns:bar="http://bar.net/ref">
	<xsl:for-each select="foo:A">
	<xsl:apply-templates select="." />
	</xsl:for-each>
	<xsl:for-each select="bar:A">
	<xsl:apply-templates select="." />
	</xsl:for-each>
	</xsl:template>

	</xsl:stylesheet>
	</source>

	<p>And a stylesheet like this:</p>

	<source>
	<?xml version="1.0"?>

	<DOC
	xmlns:foo="http://foo.com/spec"
	xmlns:bar="http://bar.net/ref">
	<foo:A>In foo namespace</foo:A>
	<bar:A>In bar namespace</bar:A>
	</DOC>
	</source>

	<p>We could still keep the same type for all <code><A></code> elements
	regardless of what namespace they are in, and use the same <code>"if"</code>
	structure within the <code>switch()</code> statement above. The other option
	is to assign different types to <code><foo:A></code> and
	<code><bar:A></code> elements.</p>

	</s2>
	</s1>