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<s1 title="Transformation API For XML">
<li><link anchor="intro">Introduction</link></li>
<li><link anchor="terminology">General Terminology</link></li>
<li><link anchor="model">Model</link></li>
<li><link anchor="patterns">Patterns</link></li>
</ul><anchor name="intro"/>
<s2 title="Introduction">
<p>This document describes the transformation API for XML (TrAX), the set of APIs contained in
<jump href="apidocs/javax/xml/transform/package-summary.html">javax.xml.transform</jump>, <jump href="apidocs/javax/xml/transform/stream/package-summary.html"></jump>, <jump href="apidocs/javax/xml/transform/dom/package-summary.html">javax.xml.transform.dom</jump>, and <jump href="apidocs/javax/xml/transform/sax/package-summary.html">javax.xml.transform.sax</jump>.</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, <jump href="">XSLT</jump>
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
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>
</s2><anchor name="terminology"/>
<s2 title="General Terminology">
<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>
<item>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
<label>Source Tree(s)</label>
<item>One or more trees that are the inputs to the
<label>Result Tree(s)</label>
<item>One or more trees that are the output of the
<item>The process of consuming a stream or tree to produce
another stream or tree.</item>
<label>Identity (or Copy) Transformation</label>
<item>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
<item>The process of taking a tree and turning it into a stream. In
some sense, a serialization is a specialized transformation.</item>
<item>The process of taking a stream and turning it into a tree. In
some sense, parsing is a specialized transformation.</item>
<item>A Transformer is the object that executes the transformation.
<label>Transformation instructions</label>
<item>Describes the transformation. A form of code, script, or
simply a declaration or series of declarations.</item>
<item>The same as "transformation instructions," except it is
likely to be used in conjunction with <jump href="">XSLT</jump>.</item>
<item>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
<item>A general term for the thing that may both process the
transformation instructions, and perform the transformation.</item>
<item>Document Object Model, specifically referring to the
<jump href="">Document Object Model
(DOM) Level 2 Specification</jump>.</item>
<item>Simple API for XML, specifically referring to the
<jump href="">SAX 2.0
</s2> <anchor name="model"/>
<s2 title="Model">
<p>The section defines the abstract model for TrAX, apart from the details
of the interfaces.</p>
<p>A TrAX <link anchor="pattern-TransformerFactory">TransformerFactory</link> is an object
that processes transformation instructions, and produces
<link anchor="pattern-Templates">Templates</link> (in the technical
terminology). A <link anchor="pattern-Templates">Templates</link>
object provides a <link anchor="pattern-Transformer">Transformer</link>, which transforms one or
more <link anchor="pattern-Source">Source</link>s into one or more
<link anchor="pattern-Result">Result</link>s.</p>
<p>To use the TrAX interface, you create a
<link anchor="pattern-TransformerFactory">TransformerFactory</link>,
which may directly provide a <link anchor="pattern-Transformer">Transformer</link>, or which can provide
<link anchor="pattern-Templates">Templates</link> from a variety of
<link anchor="pattern-Source">Source</link>s. The
<link anchor="pattern-Templates">Templates</link> object is a processed
or compiled representation of the transformation instructions, and provides a
<link anchor="pattern-Transformer">Transformer</link>. The
<link anchor="pattern-Transformer">Transformer</link> processes a
<link anchor="pattern-Transformer">Source</link> according to the
instructions found in the <link anchor="pattern-Templates">Templates</link>, and produces a
<link anchor="pattern-Result">Result</link>.</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
</s2><anchor name="patterns"/>
<s2 title="TrAX Patterns">
<p>The intent, responsibilities, and thread safety of TrAX objects:</p>
<li><link anchor="pattern-Processor">Processor</link></li>
<li><link anchor="pattern-TransformerFactory">TransformerFactory</link></li>
<li><link anchor="pattern-Templates">Templates</link></li>
<li><link anchor="pattern-Transformer">Transformer</link></li>
<li><link anchor="pattern-Source">Source</link></li>
<li><link anchor="pattern-Result">Result</link></li>
<anchor name="pattern-Processor"/><s3 title="Processor">
<item>Generic concept for the
set of objects that implement the TrAX interfaces.</item>
<item>Create compiled transformation instructions, transform
sources, and manage transformation parameters and
<label>Thread safety</label>
<item>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
</s3> <anchor name="pattern-TransformerFactory"/>
<s3 title="TransformerFactory">
<item>Serve as a vendor-neutral Processor interface for
<jump href="">XSLT</jump> and similar
<item>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.</item>
<label>Thread safety</label>
<item>A TransformerFactory may not perform mulitple concurrent
</s3><anchor name="pattern-Templates"/>
<s3 title="Templates">
<item>The runtime representation of the transformation instructions.</item>
<item>A data bag for transformation instructions; act as a factory
for Transformers.</item>
<label>Thread safety</label>
<item>Threadsafe for concurrent
usage over multiple threads once construction is complete.</item>
</s3><anchor name="pattern-Transformer"/>
<s3 title="Transformer">
<item>Act as a per-thread
execution context for transformations, act as an interface for performing the
<item>Perform the
<label>Thread safety</label>
<item>Only one instance per thread
is safe.</item>
<note>The Transformer is bound to the Templates
object that created it.</note>
</s3><anchor name="pattern-Source"/>
<s3 title="Source">
<item>Serve as a
single vendor-neutral object for multiple types of input.</item>
<item>Act as simple data holder for System IDs, DOM nodes, streams,
<label>Thread safety</label>
<item>Threadsafe concurrently over multiple
threads for read-only operations; must be synchronized for edit
</s3><anchor name="pattern-Result"/>
<s3 title="Result">
as a single object for multiple types of output, so there can be simple process
method signatures.</item>
<item>Act as simple data holder for
output stream, DOM node, ContentHandler, etc.</item>
<label>Thread safety</label>
<item>Threadsafe concurrently over multiple threads for read-only,
must be synchronized for edit.</item>