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 <head>
   <title>Transformation API For XML</title>

   <meta name="CVS"
         content="$Id: overview.html,v 1.2 2005/06/10 03:50:39 jeffsuttor Exp $" />
   <meta name="AUTHOR"
         content="Jeff.Suttor@Sun.com" />
 </head>
 <body>

 <h2>Transformation API For XML</h2>


 <h3>Introduction</h3>

 <p>This overview describes the set of APIs contained in
 	 javax.xml.transform. For the sake of brevity, these interfaces are referred to
 	 as TrAX (Transformations for XML). </p>

 <p>There is a broad need for Java applications to be able to transform XML
 	 and related tree-shaped data structures. In fact, XML is not normally very
 	 useful to an application without going through some sort of transformation,
 	 unless the semantic structure is used directly as data. Almost all XML-related
 	 applications need to perform transformations. Transformations may be described
 	 by Java code, Perl code, <A href="http://www.w3.org/TR/xslt">XSLT</A>
 	 Stylesheets, other types of script, or by proprietary formats. The inputs, one
 	 or multiple, to a transformation, may be a URL, XML stream, a DOM tree, SAX
 	 Events, or a proprietary format or data structure. The output types are the
 	 pretty much the same types as the inputs, but different inputs may need to be
 	 combined with different outputs.</p>

 <p>The great challenge of a transformation API is how to deal with all the
 	 possible combinations of inputs and outputs, without becoming specialized for
 	 any of the given types.</p>

 <p>The Java community will greatly benefit from a common API that will
 	 allow them to understand and apply a single model, write to consistent
 	 interfaces, and apply the transformations polymorphically. TrAX attempts to
 	 define a model that is clean and generic, yet fills general application
 	 requirements across a wide variety of uses. </p>


 <h3>General Terminology</h3>

 <p>This section will explain some general terminology used in this
 		document. Technical terminology will be explained in the Model section. In many
 		cases, the general terminology overlaps with the technical terminology.</p>

 <ul>
 <li>
 <p>
 <b>Tree</b>
 <br>This term, as used within this document, describes an
 			 abstract structure that consists of nodes or events that may be produced by
 			 XML. A Tree physically may be a DOM tree, a series of well balanced parse
 			 events (such as those coming from a SAX2 ContentHander), a series of requests
 			 (the result of which can describe a tree), or a stream of marked-up
 			 characters.</p>
 </li>
 <li>
 <p>
 <b>Source Tree(s)</b>
 <br>One or more trees that are the inputs to the
 			 transformation.</p>
 </li>
 <li>
 <p>
 <b>Result Tree(s)</b>
 <br>One or more trees that are the output of the
 			 transformation.</p>
 </li>
 <li>
 <p>
 <b>Transformation</b>
 <br>The processor of consuming a stream or tree to produce
 			 another stream or tree.</p>
 </li>
 <li>
 <p>
 <b>Identity (or Copy) Transformation</b>
 <br>The process of transformation from a source to a result,
 			 making as few structural changes as possible and no informational changes. The
 			 term is somewhat loosely used, as the process is really a copy. from one
 			 "format" (such as a DOM tree, stream, or set of SAX events) to
 			 another.</p>
 </li>
 <li>
 <p>
 <b>Serialization</b>
 <br>The process of taking a tree and turning it into a stream. In
 			 some sense, a serialization is a specialized transformation.</p>
 </li>
 <li>
 <p>
 <b>Parsing</b>
 <br>The process of taking a stream and turning it into a tree. In
 			 some sense, parsing is a specialized transformation.</p>
 </li>
 <li>
 <p>
 <b>Transformer</b>
 <br>A Transformer is the object that executes the transformation.
 			 </p>
 </li>
 <li>
 <p>
 <b>Transformation instructions</b>
 <br>Describes the transformation. A form of code, script, or
 			 simply a declaration or series of declarations.</p>
 </li>
 <li>
 <p>
 <b>Stylesheet</b>
 <br>The same as "transformation instructions," except it is
 			 likely to be used in conjunction with <A href="http://www.w3.org/TR/xslt">XSLT</A>.</p>
 </li>
 <li>
 <p>
 <b>Templates</b>
 <br>Another form of "transformation instructions." In the TrAX
 			 interface, this term is used to describe processed or compiled transformation
 			 instructions. The Source flows through a Templates object to be formed into the
 			 Result.</p>
 </li>
 <li>
 <p>
 <b>Processor</b>
 <br>A general term for the thing that may both process the
 			 transformation instructions, and perform the transformation.</p>
 </li>
 <li>
 <p>
 <b>DOM</b>
 <br>Document Object Model, specifically referring to the
 			 <A href="#http://www.w3.org/TR/DOM-Level-2%20">Document Object Model
 			 (DOM) Level 2 Specification</A>.</p>
 </li>
 <li>
 	<p>
 		<b>SAX</b><br>
 		Simple API for XML, specifically referring to the <a href="http://sax.sourceforge.net/">SAX 2.0.2 release</a>.
 	</p>
 </li>
 </ul>


 <h3>Model</h3>

 <p>The section defines the abstract model for TrAX, apart from the details
 	 of the interfaces.</p>

 <p>A TRaX <A href="#pattern-TransformerFactory">TransformerFactory</A> is an object
 	 that processes transformation instructions, and produces
 	 <A href="#pattern-Templates">Templates</A> (in the technical
 	 terminology). A <A href="#pattern-Templates">Templates</A>
 	 object provides a <A href="#pattern-Transformer">Transformer</A>, which transforms one or
 	 more <A href="#pattern-Source">Source</A>s into one or more
 	 <A href="#pattern-Result">Result</A>s.</p>

 <p>To use the TRaX interface, you create a
 	 <A href="#pattern-TransformerFactory">TransformerFactory</A>,
 	 which may directly provide a <A href="#pattern-Transformers">Transformers</A>, or which can provide
 	 <A href="#pattern-Templates">Templates</A> from a variety of
 	 <A href="#pattern-Source">Source</A>s. The
 	 <A href="#pattern-Templates">Templates</A> object is a processed
 	 or compiled representation of the transformation instructions, and provides a
 	 <A href="#pattern-Transformer">Transformer</A>. The
 	 <A href="#pattern-Transformer">Transformer</A> processes a
 	 <A href="#pattern-Transformer">Source</A> according to the
 	 instructions found in the <A href="#pattern-Templates">Templates</A>, and produces a
 	 <A href="#pattern-Result">Result</A>.</p>

 <p>The process of transformation from a tree, either in the form of an
 	 object model, or in the form of parse events, into a stream, is known as
 	 <code>serialization</code>. We believe this is the most suitable term for
 	 this process, despite the overlap with Java object serialization.</p>

 <H3>TRaX Patterns</H3>
 <ul>
 <p>
 <b><a name="pattern-Processor">Processor</a></b>
 <br>
 <br>
 <i>Intent: </i>Generic concept for the
   set of objects that implement the TrAX interfaces.<br>
 <i>Responsibilities: </i>Create compiled transformation instructions, transform
   sources, and manage transformation parameters and
   properties.<br>
 <i>Thread safety: </i>Only the Templates object can be
   used concurrently in multiple threads. The rest of the processor does not do
   synchronized blocking, and so may not be used to perform multiple concurrent
   operations. Different Processors can be used concurrently by different
   threads.</p>
 <p>
 <b><a name="pattern-TransformerFactory">TransformerFactory</a></b>
 <br>
 <br>
 <i>Intent: </i>Serve as a vendor-neutral Processor interface for
   <A href="http://www.w3.org/TR/xslt">XSLT</A> and similar
   processors.<br>
 <i>Responsibilities: </i>Serve as a factory for a concrete
   implementation of an TransformerFactory, serve as a direct factory for
   Transformer objects, serve as a factory for Templates objects, and manage
   processor specific features.<br>
 <i>Thread safety: </i>A
   TransformerFactory may not perform mulitple concurrent
   operations.</p>
 <p>
 <b><a name="pattern-Templates">Templates</a></b>
 <br>
 <br>
 <i>Intent: </i>The
   runtime representation of the transformation instructions.<br>
 <i>Responsibilities: </i>A data bag for transformation instructions; act as a factory
   for Transformers.<br>
 <i>Thread safety: </i>Threadsafe for concurrent
   usage over multiple threads once construction is complete.</p>
 <p>
 <b><a name="pattern-Transformer">Transformer</a></b>
 <br>
 <br>
 <i>Intent: </i>Act as a per-thread
   execution context for transformations, act as an interface for performing the
   transformation.<br>
 <i>Responsibilities: </i>Perform the
   transformation.<br>
 <i>Thread safety: </i>Only one instance per thread
   is safe.<br>
 <i>Notes: </i>The Transformer is bound to the Templates
   object that created it.</p>
 <p>
 <b><a name="pattern-Source">Source</a></b>
 <br>
 <br>
 <i>Intent: </i>Serve as a
   single vendor-neutral object for multiple types of input.<br>
 <i>Responsibilities: </i>Act as simple data holder for System IDs, DOM nodes, streams,
   etc.<br>
 <i>Thread safety: </i>Threadsafe concurrently over multiple
   threads for read-only operations; must be synchronized for edit
   operations.</p>
 <p>
 <b><a name="pattern-Result">Result</a></b>
 <br>
 <br>
 <i>Potential alternate name: </i>ResultTarget<br>
 <i>Intent: </i>Serve
   as a single object for multiple types of output, so there can be simple process
   method signatures.<br>
 <i>Responsibilities: </i>Act as simple data holder for
   output stream, DOM node, ContentHandler, etc.<br>
 <i>Thread safety: </i>Threadsafe concurrently over multiple threads for read-only,
   must be synchronized for edit.</p>
 </ul>


 </body>
 </html>
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	DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

	This code is free software; you can redistribute it and/or modify it
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	published by the Free Software Foundation. Oracle designates this
	particular file as subject to the "Classpath" exception as provided
	by Oracle in the LICENSE file that accompanied this code.

	This code is distributed in the hope that it will be useful, but WITHOUT
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	"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

	<html xmlns="http://www.w3.org/1999/xhtml">

	<head>
	<title>Transformation API For XML</title>

	<meta name="CVS"
	content="$Id: overview.html,v 1.2 2005/06/10 03:50:39 jeffsuttor Exp $" />
	<meta name="AUTHOR"
	content="Jeff.Suttor@Sun.com" />
	</head>
	<body>

	<h2>Transformation API For XML</h2>


	<h3>Introduction</h3>

	<p>This overview describes the set of APIs contained in
	javax.xml.transform. For the sake of brevity, these interfaces are referred to
	as TrAX (Transformations for XML). </p>

	<p>There is a broad need for Java applications to be able to transform XML
	and related tree-shaped data structures. In fact, XML is not normally very
	useful to an application without going through some sort of transformation,
	unless the semantic structure is used directly as data. Almost all XML-related
	applications need to perform transformations. Transformations may be described
	by Java code, Perl code, <A href="http://www.w3.org/TR/xslt">XSLT</A>
	Stylesheets, other types of script, or by proprietary formats. The inputs, one
	or multiple, to a transformation, may be a URL, XML stream, a DOM tree, SAX
	Events, or a proprietary format or data structure. The output types are the
	pretty much the same types as the inputs, but different inputs may need to be
	combined with different outputs.</p>

	<p>The great challenge of a transformation API is how to deal with all the
	possible combinations of inputs and outputs, without becoming specialized for
	any of the given types.</p>

	<p>The Java community will greatly benefit from a common API that will
	allow them to understand and apply a single model, write to consistent
	interfaces, and apply the transformations polymorphically. TrAX attempts to
	define a model that is clean and generic, yet fills general application
	requirements across a wide variety of uses. </p>


	<h3>General Terminology</h3>

	<p>This section will explain some general terminology used in this
	document. Technical terminology will be explained in the Model section. In many
	cases, the general terminology overlaps with the technical terminology.</p>

	<ul>
	<li>
	<p>
	<b>Tree</b>
	<br>This term, as used within this document, describes an
	abstract structure that consists of nodes or events that may be produced by
	XML. A Tree physically may be a DOM tree, a series of well balanced parse
	events (such as those coming from a SAX2 ContentHander), a series of requests
	(the result of which can describe a tree), or a stream of marked-up
	characters.</p>
	</li>
	<li>
	<p>
	<b>Source Tree(s)</b>
	<br>One or more trees that are the inputs to the
	transformation.</p>
	</li>
	<li>
	<p>
	<b>Result Tree(s)</b>
	<br>One or more trees that are the output of the
	transformation.</p>
	</li>
	<li>
	<p>
	<b>Transformation</b>
	<br>The processor of consuming a stream or tree to produce
	another stream or tree.</p>
	</li>
	<li>
	<p>
	<b>Identity (or Copy) Transformation</b>
	<br>The process of transformation from a source to a result,
	making as few structural changes as possible and no informational changes. The
	term is somewhat loosely used, as the process is really a copy. from one
	"format" (such as a DOM tree, stream, or set of SAX events) to
	another.</p>
	</li>
	<li>
	<p>
	<b>Serialization</b>
	<br>The process of taking a tree and turning it into a stream. In
	some sense, a serialization is a specialized transformation.</p>
	</li>
	<li>
	<p>
	<b>Parsing</b>
	<br>The process of taking a stream and turning it into a tree. In
	some sense, parsing is a specialized transformation.</p>
	</li>
	<li>
	<p>
	<b>Transformer</b>
	<br>A Transformer is the object that executes the transformation.
	</p>
	</li>
	<li>
	<p>
	<b>Transformation instructions</b>
	<br>Describes the transformation. A form of code, script, or
	simply a declaration or series of declarations.</p>
	</li>
	<li>
	<p>
	<b>Stylesheet</b>
	<br>The same as "transformation instructions," except it is
	likely to be used in conjunction with <A href="http://www.w3.org/TR/xslt">XSLT</A>.</p>
	</li>
	<li>
	<p>
	<b>Templates</b>
	<br>Another form of "transformation instructions." In the TrAX
	interface, this term is used to describe processed or compiled transformation
	instructions. The Source flows through a Templates object to be formed into the
	Result.</p>
	</li>
	<li>
	<p>
	<b>Processor</b>
	<br>A general term for the thing that may both process the
	transformation instructions, and perform the transformation.</p>
	</li>
	<li>
	<p>
	<b>DOM</b>
	<br>Document Object Model, specifically referring to the
	<A href="#http://www.w3.org/TR/DOM-Level-2%20">Document Object Model
	(DOM) Level 2 Specification</A>.</p>
	</li>
	<li>
	<p>
	<b>SAX</b><br>
	Simple API for XML, specifically referring to the <a href="http://sax.sourceforge.net/">SAX 2.0.2 release</a>.
	</p>
	</li>
	</ul>



	<h3>Model</h3>

	<p>The section defines the abstract model for TrAX, apart from the details
	of the interfaces.</p>

	<p>A TRaX <A href="#pattern-TransformerFactory">TransformerFactory</A> is an object
	that processes transformation instructions, and produces
	<A href="#pattern-Templates">Templates</A> (in the technical
	terminology). A <A href="#pattern-Templates">Templates</A>
	object provides a <A href="#pattern-Transformer">Transformer</A>, which transforms one or
	more <A href="#pattern-Source">Source</A>s into one or more
	<A href="#pattern-Result">Result</A>s.</p>

	<p>To use the TRaX interface, you create a
	<A href="#pattern-TransformerFactory">TransformerFactory</A>,
	which may directly provide a <A href="#pattern-Transformers">Transformers</A>, or which can provide
	<A href="#pattern-Templates">Templates</A> from a variety of
	<A href="#pattern-Source">Source</A>s. The
	<A href="#pattern-Templates">Templates</A> object is a processed
	or compiled representation of the transformation instructions, and provides a
	<A href="#pattern-Transformer">Transformer</A>. The
	<A href="#pattern-Transformer">Transformer</A> processes a
	<A href="#pattern-Transformer">Source</A> according to the
	instructions found in the <A href="#pattern-Templates">Templates</A>, and produces a
	<A href="#pattern-Result">Result</A>.</p>

	<p>The process of transformation from a tree, either in the form of an
	object model, or in the form of parse events, into a stream, is known as
	<code>serialization</code>. We believe this is the most suitable term for
	this process, despite the overlap with Java object serialization.</p>

	<H3>TRaX Patterns</H3>
	<ul>
	<p>
	<b><a name="pattern-Processor">Processor</a></b>
	<br>
	<br>
	<i>Intent: </i>Generic concept for the
	set of objects that implement the TrAX interfaces.<br>
	<i>Responsibilities: </i>Create compiled transformation instructions, transform
	sources, and manage transformation parameters and
	properties.<br>
	<i>Thread safety: </i>Only the Templates object can be
	used concurrently in multiple threads. The rest of the processor does not do
	synchronized blocking, and so may not be used to perform multiple concurrent
	operations. Different Processors can be used concurrently by different
	threads.</p>
	<p>
	<b><a name="pattern-TransformerFactory">TransformerFactory</a></b>
	<br>
	<br>
	<i>Intent: </i>Serve as a vendor-neutral Processor interface for
	<A href="http://www.w3.org/TR/xslt">XSLT</A> and similar
	processors.<br>
	<i>Responsibilities: </i>Serve as a factory for a concrete
	implementation of an TransformerFactory, serve as a direct factory for
	Transformer objects, serve as a factory for Templates objects, and manage
	processor specific features.<br>
	<i>Thread safety: </i>A
	TransformerFactory may not perform mulitple concurrent
	operations.</p>
	<p>
	<b><a name="pattern-Templates">Templates</a></b>
	<br>
	<br>
	<i>Intent: </i>The
	runtime representation of the transformation instructions.<br>
	<i>Responsibilities: </i>A data bag for transformation instructions; act as a factory
	for Transformers.<br>
	<i>Thread safety: </i>Threadsafe for concurrent
	usage over multiple threads once construction is complete.</p>
	<p>
	<b><a name="pattern-Transformer">Transformer</a></b>
	<br>
	<br>
	<i>Intent: </i>Act as a per-thread
	execution context for transformations, act as an interface for performing the
	transformation.<br>
	<i>Responsibilities: </i>Perform the
	transformation.<br>
	<i>Thread safety: </i>Only one instance per thread
	is safe.<br>
	<i>Notes: </i>The Transformer is bound to the Templates
	object that created it.</p>
	<p>
	<b><a name="pattern-Source">Source</a></b>
	<br>
	<br>
	<i>Intent: </i>Serve as a
	single vendor-neutral object for multiple types of input.<br>
	<i>Responsibilities: </i>Act as simple data holder for System IDs, DOM nodes, streams,
	etc.<br>
	<i>Thread safety: </i>Threadsafe concurrently over multiple
	threads for read-only operations; must be synchronized for edit
	operations.</p>
	<p>
	<b><a name="pattern-Result">Result</a></b>
	<br>
	<br>
	<i>Potential alternate name: </i>ResultTarget<br>
	<i>Intent: </i>Serve
	as a single object for multiple types of output, so there can be simple process
	method signatures.<br>
	<i>Responsibilities: </i>Act as simple data holder for
	output stream, DOM node, ContentHandler, etc.<br>
	<i>Thread safety: </i>Threadsafe concurrently over multiple threads for read-only,
	must be synchronized for edit.</p>
	</ul>


	</body>
	</html>