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+<!DOCTYPE html
+ PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
+ "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>