dleslie 01/06/27 13:24:58
Modified: java/xdocs/sources/design design2_0_0.xml
Log:
Fixed anchors and use of <code> to enable transformation to DITA
along with the "standard" Xalan xml sources.
Revision Changes Path
1.4 +51 -46 xml-xalan/java/xdocs/sources/design/design2_0_0.xml
Index: design2_0_0.xml
===================================================================
RCS file: /home/cvs/xml-xalan/java/xdocs/sources/design/design2_0_0.xml,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -r1.3 -r1.4
--- design2_0_0.xml 2001/01/12 07:46:58 1.3
+++ design2_0_0.xml 2001/06/27 20:24:56 1.4
@@ -1,7 +1,7 @@
<?xml version="1.0"?>
-<!DOCTYPE s1 SYSTEM "sbk:/style/dtd/document.dtd">
+<!DOCTYPE s1 SYSTEM "../../style/dtd/document.dtd">
<s1 title="Xalan-J 2.0 Design">
- <p><link>Xalan-J 2.0 Design</link><img src="xmllogo.gif"
alt="xmllogo.gif"/></p>
+ <p><img src="xmllogo.gif" alt="xmllogo.gif"/></p>
<p>Author: Scott Boag<br/>State: In Progress</p>
<ul>
<li><link anchor="intro">Introduction</link></li>
@@ -23,7 +23,6 @@
<li><jump href="../apidocs/index.html">Xalan-J 2.0 Javadoc</jump></li>
</ul><anchor name="intro"/>
<s2 title="Introduction">
- <p><link>Introduction</link></p>
<p>This document presents the basic design for Xalan-J 2.0, which is a
<jump
href="http://www.awl.com/cseng/titles/0-201-89542-0/techniques/refactoring.htm";>refactoring</jump>
and redesign of the Xalan-J 1.x processor. This document will
expand and grow over time, and is also incomplete in some sections, though
hopefully overall accurate. The reader should be able to get a good overall
idea of the internal design of Xalan, and begin to understand the process flow,
and also the technical challanges.</p>
@@ -63,9 +62,10 @@
<p>Please note that the diagrams in this design document are meant to
be
useful abstractions, and may not always be exact.</p>
</s2><anchor name="requirements"/>
- <s2 title="Xalan Requirements"><p><link>Xalan
Requirements</link></p><p>These are the concrete general requirements of Xalan,
as I understand them, and covering both the Java and C++ versions. These
requirements have been built up over time by experience with product groups and
general users.</p><ol><li>Java, C++ Versions.</li><li>XSLT 1.0 conformance, and
beyond. (i.e. conform to the current W3C recommendation).</li><li>Have design
and Code understandable by Open Source Community.</li><li>Ability to
interoperate with standard APIs. (SAX2, DOM2, JAXP) [this is currently Less
of an issue with C++].</li><li>High Performance (Raw performance, Incremental
ability, Scaleability to large documents, Reduction of Garbage Collection for
the Java version.)</li><li>Tooling API (Access stylesheet data structures,
Access source node from result event, Ask runtime questions, Debugging
API).</li><li>Support addressing of XML in standalone fashion (i.e. XPath
API).</li><li>Extensibility (Ability to call Java, Ability to call JavaScript,
other languages).</li><li>Multiple data sources (JDBC, LDAP, other data
sources, Direct XML repository coupling).</li></ol></s2><anchor
name="overarch"/>
+ <s2 title="Xalan Requirements">
+ <p>These are the concrete general requirements of Xalan, as I understand
them, and covering both the Java and C++ versions. These requirements have
been built up over time by experience with product groups and general
users.</p><ol><li>Java, C++ Versions.</li><li>XSLT 1.0 conformance, and beyond.
(i.e. conform to the current W3C recommendation).</li><li>Have design and Code
understandable by Open Source Community.</li><li>Ability to interoperate with
standard APIs. (SAX2, DOM2, JAXP) [this is currently Less of an issue with
C++].</li><li>High Performance (Raw performance, Incremental ability,
Scaleability to large documents, Reduction of Garbage Collection for the Java
version.)</li><li>Tooling API (Access stylesheet data structures, Access source
node from result event, Ask runtime questions, Debugging API).</li><li>Support
addressing of XML in standalone fashion (i.e. XPath API).</li><li>Extensibility
(Ability to call Java, Ability to call JavaScript, other
languages).</li><li>Multiple data sources (JDBC, LDAP, other data sources,
Direct XML repository coupling).</li></ol></s2><anchor name="overarch"/>
<s2 title="Overview of Architecture">
- <p><link>Overview of Architecture</link></p><p>The following diagram
shows the XSLT abstract processing model. A transformation expressed in XSLT
describes rules for transforming a <jump
href="http://www.w3.org/TR/xpath#data-model";>Source Tree </jump> into a result
tree. The transformation is achieved by associating patterns with templates. A
pattern is matched against elements in the source tree. A template is
instantiated to create part of the result tree. The result tree is separate
from the source tree. The structure of the result tree can be completely
different from the structure of the source tree. In constructing the result
tree, elements from the source tree can be filtered and reordered, and
arbitrary structure can be added.
+ <p>The following diagram shows the XSLT abstract processing model. A
transformation expressed in XSLT describes rules for transforming a <jump
href="http://www.w3.org/TR/xpath#data-model";>Source Tree </jump> into a result
tree. The transformation is achieved by associating patterns with templates. A
pattern is matched against elements in the source tree. A template is
instantiated to create part of the result tree. The result tree is separate
from the source tree. The structure of the result tree can be completely
different from the structure of the source tree. In constructing the result
tree, elements from the source tree can be filtered and reordered, and
arbitrary structure can be added.
</p><p>The term "tree", as used within this document, describes an
abstract structure that consists of nodes or events
that may be produced by
@@ -76,23 +76,23 @@
<p>The internal architecture of Xalan 2.0 is divided into four major
modules, and various smaller
modules. The main modules are:</p>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/processor/package-summary.html">org.apache.xalan.processor</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/processor/package-summary.html">org.apache.xalan.processor</jump></label>
<item>The module that processes the stylesheet, and provides
the main
entry point into Xalan.</item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/templates/package-summary.html">org.apache.xalan.templates</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/templates/package-summary.html">org.apache.xalan.templates</jump></label>
<item>The module that defines the stylesheet structures,
including the
Stylesheet object, template element instructions, and
Attribute Value
Templates. </item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/transformer/package-summary.html">org.apache.xalan.transformer</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/transformer/package-summary.html">org.apache.xalan.transformer</jump></label>
<item>The module that applies the source tree to the Templates,
and
produces a result tree.</item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xpath/package-summary.html">org.apache.xpath</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xpath/package-summary.html">org.apache.xpath</jump></label>
<item>The module that processes both XPath expressions, and
XSLT Match
patterns.</item>
</gloss>
@@ -108,45 +108,44 @@
<p>In addition to the above packages, there are the following
additional
packages:</p>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/client/package-summary.html">org.apache.xalan.client</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/client/package-summary.html">org.apache.xalan.client</jump></label>
<item>This package has a client applet. I suspect this should
be moved
into the samples directory.</item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/extensions/package-summary.html">org.apache.xalan.extensions</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/extensions/package-summary.html">org.apache.xalan.extensions</jump></label>
<item>This holds classes belonging to the Xalan extensions
mechanism,
which allows Java code and script to be called from within a
stylesheet.</item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/lib/package-summary.html">org.apache.xalan.lib</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/lib/package-summary.html">org.apache.xalan.lib</jump></label>
<item>This is the built-in Xalan extensions library, which holds
extensions such as Redirect (which allows a stylesheet to
produce multiple
output files).</item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/res/package-summary.html">org.apache.xalan.res</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/res/package-summary.html">org.apache.xalan.res</jump></label>
<item>This holds resource files needed by Xalan, such as error
message
resources.</item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/trace/package-summary.html">org.apache.xalan.trace</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/trace/package-summary.html">org.apache.xalan.trace</jump></label>
<item>This package contains classes and interfaces that allow a
caller to
add trace listeners to the transformation, allowing an
interface to XSLT
debuggers and similar tools.</item>
</gloss>
<gloss>
- <label><code><jump
href="../apidocs/org/apache/xalan/xslt/package-summary.html">org.apache.xalan.xslt</jump></code></label>
+ <label><jump
href="../apidocs/org/apache/xalan/xslt/package-summary.html">org.apache.xalan.xslt</jump></label>
<item>This package holds the Xalan2 command line
processor.</item>
</gloss>
<p>A more conceptual view of this architecture is as follows:</p><p><img
src="conceptual.gif" alt="Picture of conceptual
architecture."/></p></s2><anchor name="process"/>
<s2 title="Process Module">
- <p><link>Processor Module</link></p>
- <p>The <code><jump
href="../apidocs/org/apache/xalan/processor/package-summary.html">org.apache.xalan.processor</jump></code>
module implements the
- <code><jump
href="../apidocs/javax/xml/transform/TransformerFactory.html">javax.xml.transform.TransformerFactory</jump></code>
interface, which provides a
+ <p>The <jump
href="../apidocs/org/apache/xalan/processor/package-summary.html">org.apache.xalan.processor</jump>
module implements the
+ <jump
href="../apidocs/javax/xml/transform/TransformerFactory.html">javax.xml.transform.TransformerFactory</jump>
interface, which provides a
factory method for creating a concrete Processor instance, and
provides methods
- for creating a <code><jump
href="../apidocs/javax/xml/transform/Templates.html">javax.xml.transform.Templates</jump></code>
instance, which, in
+ for creating a <jump
href="../apidocs/javax/xml/transform/Templates.html">javax.xml.transform.Templates</jump>
instance, which, in
Xalan and XSLT terms, is the Stylesheet. Thus the task of the
process module is
to read the XSLT input in the form of a file, stream, SAX
events, or a DOM
tree, and produce a Templates/Stylesheet object.</p>
@@ -157,39 +156,38 @@
module that can be created in a generalized fashion. This makes
the validation
object-to-class associations centralized and declarative.</p>
<p>The schema's root class is
- <code><jump
href="../apidocs/org/apache/xalan/processor/XSLTSchema.html">org.apache.xalan.processor.XSLTSchema</jump></code>,
and it is here that the
+ <jump
href="../apidocs/org/apache/xalan/processor/XSLTSchema.html">org.apache.xalan.processor.XSLTSchema</jump>,
and it is here that the
XSLT schema structure is defined. XSLTSchema uses
- <code><jump
href="../apidocs/org/apache/xalan/processor/XSLTElementDef.html">org.apache.xalan.processor.XSLTElementDef</jump></code>
to define elements, and
- <code><jump
href="../apidocs/org/apache/xalan/processor/XSLTAttributeDef.html">org.apache.xalan.processor.XSLTAttributeDef</jump></code>
to define attributes.
+ <jump
href="../apidocs/org/apache/xalan/processor/XSLTElementDef.html">org.apache.xalan.processor.XSLTElementDef</jump>
to define elements, and
+ <jump
href="../apidocs/org/apache/xalan/processor/XSLTAttributeDef.html">org.apache.xalan.processor.XSLTAttributeDef</jump>
to define attributes.
Both classes hold the allowed namespace, local name, and type
of element or
attribute. The XSLTElementDef also holds a reference to a
- <code><jump
href="../apidocs/org/apache/xalan/processor/XSLTElementProcessor.html">org.apache.xalan.processor.XSLTElementProcessor</jump></code>,
and a sometimes a
+ <jump
href="../apidocs/org/apache/xalan/processor/XSLTElementProcessor.html">org.apache.xalan.processor.XSLTElementProcessor</jump>,
and a sometimes a
<code>Class</code> object, with which it can create objects
that derive from
- <code><jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html">org.apache.xalan.templates.ElemTemplateElement</jump></code>.
In addition, the
+ <jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html">org.apache.xalan.templates.ElemTemplateElement</jump>.
In addition, the
XSLTElementDef instance holds a list of XSLTElementDef
instances that define
legal elements or character events that are allowed as children
of the given
element.</p>
- <p>The implementation of the <code><jump
href="../apidocs/javax/xml/transform/TransformerFactory.html">javax.xml.transform.TransformerFactory</jump></code>
- interface is in <code><jump
href="../apidocs/org/apache/xalan/processor/TransformerFactoryImpl.html">org.apache.xalan.processor.TransformerFactoryImpl</jump></code>,
- which creates a <code><jump
href="../apidocs/org/apache/xalan/processor/StylesheetHandler.html">org.apache.xalan.processor.StylesheetHandler</jump></code>
+ <p>The implementation of the <jump
href="../apidocs/javax/xml/transform/TransformerFactory.html">javax.xml.transform.TransformerFactory</jump>
+ interface is in <jump
href="../apidocs/org/apache/xalan/processor/TransformerFactoryImpl.html">org.apache.xalan.processor.TransformerFactoryImpl</jump>,
+ which creates a <jump
href="../apidocs/org/apache/xalan/processor/StylesheetHandler.html">org.apache.xalan.processor.StylesheetHandler</jump>
instance. This instance acts as the ContentHandler for the
parse events, and is
- handed to the <code><jump
href="../apidocs/org/xml/sax/XMLReader.html">org.xml.sax.XMLReader</jump></code>,
which the StylesheetProcessor
+ handed to the <jump
href="../apidocs/org/xml/sax/XMLReader.html">org.xml.sax.XMLReader</jump>,
which the StylesheetProcessor
uses to parse the XSLT document. The
<code>StylesheetHandler</code> then receives the parse
events, which maintains the state of the construction, and
passes the events on
to the appropriate <code>XSLTElementProcessor</code> for the
given event, as dictated by the
<code>XSLTElementDef</code> that is associated with the given
event.</p>
</s2><anchor name="templates"/>
<s2 title="Templates Module">
- <p><link>Templates Module</link></p>
- <p>The <code><jump
href="../apidocs/org/apache/xalan/templates/package-summary.html">org.apache.xalan.templates</jump></code>
module implements the
- <code><jump
href="../apidocs/javax/xml/transform/Templates.html">javax.xml.transform.Templates</jump></code>
interface, and defines a set of
+ <p>The <jump
href="../apidocs/org/apache/xalan/templates/package-summary.html">org.apache.xalan.templates</jump>
module implements the
+ <jump
href="../apidocs/javax/xml/transform/Templates.html">javax.xml.transform.Templates</jump>
interface, and defines a set of
classes that represent a Stylesheet. The primary purpose of
this module is to
hold stylesheet data, not to perform procedural tasks
associated with the
construction of the data, nor tasks associated with the
transformation itself.
</p>
- <p>The base class of all templates objects that are associated with an
XSLT element is the <code><jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html">ElemTemplateElement</jump></code>
object, which in turn implements <code><jump
href="../apidocs/org/apache/xml/utils/UnImplNode.html">UnImplNode</jump></code>.
A <code>ElemTemplateElement</code> object must be immutable once it's
constructed, so that it may be shared among multiple threads concurrently.
Ideally, a <code>ElemTemplateElement</code> should be a data object only, and
be used via a visitor pattern. However, in practice this is impractical,
because it would cause too much data exposure and would have a significant
impact on performance. Therefore, each <code>ElemTemplateElement</code> class
has an <code><jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html#execute(org.apache.xalan.transformer.TransformerImpl,
org.w3c.dom.Node, org.apache.xml.utils.QName)">execute</jump></code> method
where it performs it's transformation duties. A
<code>ElemTemplateElement</code> also knows it's position in the source
stylesheet, and can answer questions about current namespace nodes.</p><p>A
<code><jump
href="../apidocs/org/apache/xalan/templates/StylesheetRoot.html">StylesheetRoot</jump></code>,
which implements the
- <code>Templates</code> interface, is a type of <code><jump
href="../apidocs/org/apache/xalan/templates/StylesheetComposed.html">StylesheetComposed</jump></code>,
- which is a <code><jump
href="../apidocs/org/apache/xalan/templates/Stylesheet.html">Stylesheet</jump></code>
composed of itself and all included
+ <p>The base class of all templates objects that are associated with an
XSLT element is the <jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html">ElemTemplateElement</jump>
object, which in turn implements <jump
href="../apidocs/org/apache/xml/utils/UnImplNode.html">UnImplNode</jump>. A
<code>ElemTemplateElement</code> object must be immutable once it's
constructed, so that it may be shared among multiple threads concurrently.
Ideally, a <code>ElemTemplateElement</code> should be a data object only, and
be used via a visitor pattern. However, in practice this is impractical,
because it would cause too much data exposure and would have a significant
impact on performance. Therefore, each <code>ElemTemplateElement</code> class
has an <jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html#execute(org.apache.xalan.transformer.TransformerImpl,
org.w3c.dom.Node, org.apache.xml.utils.QName)">execute</jump> method where it
performs it's transformation duties. A <code>ElemTemplateElement</code> also
knows it's position in the source stylesheet, and can answer questions about
current namespace nodes.</p><p>A <jump
href="../apidocs/org/apache/xalan/templates/StylesheetRoot.html">StylesheetRoot</jump>,
which implements the
+ <code>Templates</code> interface, is a type of <jump
href="../apidocs/org/apache/xalan/templates/StylesheetComposed.html">StylesheetComposed</jump>,
+ which is a <jump
href="../apidocs/org/apache/xalan/templates/Stylesheet.html">Stylesheet</jump>
composed of itself and all included
<code>Stylesheet</code> objects. A <code>StylesheetRoot</code>
has a global
imports list, which is a list of all imported
<code>StylesheetComposed</code>
instances. From each <code>StylesheetComposed</code> object,
one can iterate
@@ -210,45 +208,52 @@
</s2><anchor name="transformer"/>
<s2 title="Transformer Module">
- <p><link>Transformer Module</link></p>
- <p>The <jump
href="../apidocs/org/apache/xalan/transformer/package-summary.html">Transformer</jump>
module is in charge of run-time transformations. The <jump
href="../apidocs/org/apache/xalan/transformer/TransformerImpl.html">TransformerImpl</jump>
object, which implements the TrAX <jump
href="../apidocs/javax/xml/transform/Transformer.html">Transformer</jump>
interface, and has an association with a <jump
href="../apidocs/org/apache/xalan/templates/StylesheetRoot.html">StylesheetRoot</jump>
object, begins the processing of the source tree (or provides a <jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html";>ContentHandler</jump>
reference via the<code><jump
href="../apidocs/org/apache/xalan/stree/SourceTreeHandler.html">SourceTreeHandler</jump></code>),
and performs the transformation. The Transformer package does as much of the
transformation as it can, but element level operations are generally performed
in the <jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html#execute(org.apache.xalan.transformer.TransformerImpl,
org.w3c.dom.Node,
org.apache.xalan.utils.QName)">ElemTemplateElement.execute(...)</jump>
methods.</p><p>Result Tree events are fed into a <jump
href="../apidocs/org/apache/xalan/transformer/ResultTreeHandler.html">ResultTreeHandler</jump>
object, which acts as a layer between the direct calls to the result
+ <p>The <jump
href="../apidocs/org/apache/xalan/transformer/package-summary.html">Transformer</jump>
module is in charge of run-time transformations. The <jump
href="../apidocs/org/apache/xalan/transformer/TransformerImpl.html">TransformerImpl</jump>
object, which implements the TrAX <jump
href="../apidocs/javax/xml/transform/Transformer.html">Transformer</jump>
interface, and has an association with a <jump
href="../apidocs/org/apache/xalan/templates/StylesheetRoot.html">StylesheetRoot</jump>
object, begins the processing of the source tree (or provides a <jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html";>ContentHandler</jump>
reference via the <jump
href="../apidocs/org/apache/xalan/stree/SourceTreeHandler.html">SourceTreeHandler</jump>),
and performs the transformation. The Transformer package does as much of the
transformation as it can, but element level operations are generally performed
in the <jump
href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html#execute(org.apache.xalan.transformer.TransformerImpl,
org.w3c.dom.Node,
org.apache.xalan.utils.QName)">ElemTemplateElement.execute(...)</jump>
methods.</p><p>Result Tree events are fed into a <jump
href="../apidocs/org/apache/xalan/transformer/ResultTreeHandler.html">ResultTreeHandler</jump>
object, which acts as a layer between the direct calls to the result
tree content handler (often a <jump
href="../apidocs/org/apache/xalan/serialize/package-summary.html">Serializer</jump>),
and the <code>Transformer</code>. For one thing,
we have to delay the call to
startElement(name, atts) because of the
xsl:attribute and xsl:copy calls. In other words,
the attributes have to be fully collected before you
- can call startElement.</p><p>Other important classes in this package
are:</p><gloss><label>CountersTable and Counter</label><item>The <code><jump
href="../apidocs/org/apache/xalan/transformer/Counter.html">Counter</jump></code>
class does incremental counting for support of xsl:number.
+ can call startElement.</p><p>Other important classes in this package
are:</p><gloss><label>CountersTable and Counter</label><item>The <jump
href="../apidocs/org/apache/xalan/transformer/Counter.html">Counter</jump>
class does incremental counting for support of xsl:number.
This class stores a cache of counted nodes (m_countNodes).
It tries to cache the counted nodes in document order...
- the node count is based on its position in the cache list. The <code><jump
href="../apidocs/org/apache/xalan/transformer/CountersTable.html">CountersTable</jump></code>
class is a table of counters, keyed by <code><jump
href="../apidocs/org/apache/xalan/templates/ElemNumber.html">ElemNumber</jump></code>
objects, each
+ the node count is based on its position in the cache list. The <jump
href="../apidocs/org/apache/xalan/transformer/CountersTable.html">CountersTable</jump>
class is a table of counters, keyed by <jump
href="../apidocs/org/apache/xalan/templates/ElemNumber.html">ElemNumber</jump>
objects, each
of which has a list of <code>Counter</code>
objects.</item></gloss><gloss><label>KeyIterator, KeyManager, and
KeyTable</label><item>These classes handle mapping of keys declared with the
xsl:key element. They attempt to work incrementally, locating nodes on request
but indexing all as they traverse the tree, and stopping when the requested
node is found. If a requested node is not found, then the entire tree will be
traversed. Such is the nature of
xsl:key.</item></gloss><gloss><label>TransformState</label><item>This interface
is meant to be used by a consumer of SAX2 events produced by Xalan, and enables
the consumer
to get information about the state of the transform. It
is primarily intended as a tooling interface.</item></gloss><p>Even though
the following modules are defined in the <code>org.apache.xalan</code> package,
instead of the transformer package, they are defined in this section as they
are mostly related to runtime transformation.</p><anchor name="stree"/>
- <s3 title="Stree Module"><p><link>Stree Module [And discussions about
streaming]</link></p><p>The Stree module implements the default <jump
href="http://www.w3.org/TR/xpath#data-model";>Source Tree </jump> for Xalan,
that is to be transformed. It implements read-only <jump
href="http://www.w3.org/TR/DOM-Level-2/";>DOM2</jump> interfaces, and provides
some information needed for fast transforms, such as document order indexes.
It also attempts to allow an incremental transform by launching the transform
on a secondary thread as soon as the SAX2 <jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html#startDocument()">StartDocument</jump>
event has occurred. When the transform requests a node, and the node is not
present, the getFirstChild and GetNextSibling methods will wait until the child
node has arrived, or an <jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html#endElement(java.lang.String,%20java.lang.String,%20java.lang.String)">endElement</jump>
event has occurred.</p><p>Note that the secondary thread is an issue. It
would be better to do the same thing as described above on a single thread, but
using the parser in 'pull' mode, or simply with a parseNext method so the parse
would occur in blocks. However, this model would only be possible</p><p>This
kind of incrementality is not perfect because it still requires an entire
source tree to be concretely built. There have been a lot of good discussions
on the xalan-dev list about how to do static analysis of a stylesheet, and be
able to allocate only the nodes needed by the transform, while they are needed
(or not allocate source objects at all).</p></s3><s3 title="Serializer
Module"><p><link>Serializer Module</link></p><p>XML serialization is a term
used for turning a tree or set of events into a stream, and should not be
confused with Java object serialization. The Xalan serializers implement the
<jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html";>ContentHandler</jump>
to turn parser events coming from the transform, into a stream of XML, HTML,
or plain text. The serializers also implement the <code><jump
href="../apidocs/org/apache/xalan/serializer/Serializer.html">Serializer</jump></code>
which allows the transform process to set XSLT output properties and the
output stream or Writer.</p></s3><s3 title="Extensions
Module"><p><link>Extensions Module</link></p><p>This package contains an
implementation of Xalan Extension Mechanism, which uses the <jump
href="http://oss.software.ibm.com/developerworks/opensource/bsf/";>Bean
Scripting Framework</jump>.
+ <s3 title="Stree Module [and discussions about streaming]">
+ <p>The Stree module implements the default <jump
href="http://www.w3.org/TR/xpath#data-model";>Source Tree </jump> for Xalan,
that is to be transformed. It implements read-only <jump
href="http://www.w3.org/TR/DOM-Level-2/";>DOM2</jump> interfaces, and provides
some information needed for fast transforms, such as document order indexes.
It also attempts to allow an incremental transform by launching the transform
on a secondary thread as soon as the SAX2 <jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html#startDocument()">StartDocument</jump>
event has occurred. When the transform requests a node, and the node is not
present, the getFirstChild and GetNextSibling methods will wait until the child
node has arrived, or an <jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html#endElement(java.lang.String,%20java.lang.String,%20java.lang.String)">endElement</jump>
event has occurred.</p><p>Note that the secondary thread is an issue. It
would be better to do the same thing as described above on a single thread, but
using the parser in 'pull' mode, or simply with a parseNext method so the parse
would occur in blocks. However, this model would only be possible</p><p>This
kind of incrementality is not perfect because it still requires an entire
source tree to be concretely built. There have been a lot of good discussions
on the xalan-dev list about how to do static analysis of a stylesheet, and be
able to allocate only the nodes needed by the transform, while they are needed
(or not allocate source objects at all).</p></s3>
+<anchor name="serializer"/>
+<s3 title="Serializer Module">
+<p>XML serialization is a term used for turning a tree or set of events into
a stream, and should not be confused with Java object serialization. The Xalan
serializers implement the <jump
href="http://www.megginson.com/SAX/Java/javadoc/org/xml/sax/ContentHandler.html";>ContentHandler</jump>
to turn parser events coming from the transform, into a stream of XML, HTML,
or plain text. The serializers also implement the <jump
href="../apidocs/org/apache/xalan/serializer/Serializer.html">Serializer</jump>
which allows the transform process to set XSLT output properties and the output
stream or Writer.</p></s3><anchor name="extensions"/>
+<s3 title="Extensions Module">
+<p>This package contains an implementation of Xalan Extension Mechanism,
which uses the <jump
href="http://oss.software.ibm.com/developerworks/opensource/bsf/";>Bean
Scripting Framework</jump>.
The Bean Scripting Framework (BSF) is an architecture for incorporating
scripting into Java applications and applets. Scripting languages such as
Netscape Rhino (Javascript), VBScript, Perl, Tcl, Python, NetRexx and Rexx can
be used to augment XSLT's functionality. In addition, the Xalan extension
mechanism allows use of Java classes. See the <jump
href="http://xml.apache.org/xalan/extensions.html";>Xalan-J 2 extension
documentation</jump> for a description of using extensions in a stylesheet.
Please note that the W3C XSL Working Group is working on a specification for
standard extension bindings, and this module will change to follow that
specification. </p><p>[More needed... -sb]</p></s3></s2><anchor name="xpath"/>
<s2 title="XPath Module">
- <p><link>XPath Module</link></p>
<p>This module is pulled out of the Xalan package, and put in the
org.apache package, to emphasize that the intention is that this package can be
used independently of the XSLT engine, even though it has dependencies on the
Xalan utils module.</p><p><img src="org_apache.gif" alt="xalan --->
xpath"/></p>
<p>The XPath module first compiles the XPath strings into expression
trees, and then executes these expressions via a call to the XPath execute(...)
function. </p> <p>Major classes
are:</p><gloss><label>XPath</label><item>Represents a compiled XPath. Major
function is <code>XObject execute(XPathContext xctxt, Node contextNode,
- PrefixResolver
namespaceContext).</code></item></gloss><gloss><label>XPathAPI</label><item>The
methods in this class are convenience methods into the
+ PrefixResolver
namespaceContext)</code>.</item></gloss><gloss><label>XPathAPI</label><item>The
methods in this class are convenience methods into the
low-level XPath
API.</item></gloss><gloss><label>XPathContext</label><item>Used as the runtime
execution context for
XPath.</item></gloss><gloss><label>DOMHelper</label><item>Used as a helper for
handling DOM issues. May be subclassed to take advantage
of specific DOM
implementations.</item></gloss><gloss><label>SourceTreeManager</label><item>bottlenecks
all management of source trees. The methods
in this class should allow easy garbage collection of source
- trees, and should centralize parsing for those source
trees.</item></gloss><gloss><label>Expression</label><item>The base-class of
all expression objects, allowing polymorphic behaviors.</item></gloss><p>The
general architecture of the XPath module is divided into the compiler, and
categories of expression objects.</p><p><img src="xpath.gif" alt="xpath
modules"/></p><p>The most important module is the axes module. This module
implements the DOM2 <jump
href="http://www.w3.org/TR/DOM-Level-2/traversal.html#Iterator-overview";>NodeIterator</jump>
interface, and is meant to allow XPath clients to either override the default
behavior or to replace this behavior.</p><p>The <code><jump
href="../apidocs/org/apache/xpath/axes/LocPathIterator.html">LocPathIterator</jump></code>
and <code><jump
href="../apidocs/org/apache/xpath/axes/UnionPathIterator.html">UnionPathIterator</jump></code>
classes implement the <jump
href="http://www.w3.org/TR/DOM-Level-2/java-binding.html#org.w3c.dom.traversal.NodeIterator";>NodeIterator</jump>
interface, and polymorphically use <code><jump
href="../apidocs/org/apache/xpath/axes/AxesWalker.html">AxesWalker</jump></code>
derived objects to execute each step in the path. The whole trick is to
execute the <code>LocationPath</code> in depth-first document order so that
nodes can be found without necessarily looking ahead or performing a
breadth-first search. Because a document order depth-first search requires
state to be saved for many expressions, the default operations create "Waiter"
clones that have to wait while the main <code>AxesWalkers</code> traverses
child nodes (think carefully about what happens when a "//foo/baz" expression
is executed). Optimization is done by implementing specialized iterators and
<code>AxesWalkers</code> for certain types of operations. The decision as to
what type of iterator or walker will be created is done in the <code><jump
href="../apidocs/org/apache/xpath/axes/WalkerFactory.html">WalkerFactory</jump></code>
class.</p><p>[Frankly, the implementation of the default AxesWalker, with it's
waiters, is the one totally incomprehensible part of Xalan. It gets especially
difficult because you can not look to the node ahead. I would be very
interested if any rocket scientists out there can come up with a better
algorithm.]</p><anchor name="xpathdbconn"/><s3 title="XPath Database
Connection"><p><link>XPath Direct Database Connections</link></p><p>An
important part of the XPath design in both Xalan 1 and Xalan 2, is to enable
database connections to be used as drivers directly to the XPath <jump
href="http://www.w3.org/TR/xpath#location-paths";>LocationPath</jump> handling.
This allows databases to be directly connected to the transform, and be able to
take advantage of internal indexing and the like. While in Xalan 1 this was
done via the <jump
href="http://xml.apache.org/xalan/apidocs/org/apache/xalan/xpath/XLocator.html";>XLocator</jump>
interface, in Xalan 2 this interface is no longer used, and has been replaced
by the DOM2 <jump
href="http://www.w3.org/TR/DOM-Level-2/traversal.html#Iterator-overview";>NodeIterator</jump>
interface. An application or extension should be able to install their own
NodeIterator for a given document.</p><p><img src="data.gif"
alt="data.gif"/></p><p>[More to do]</p></s3></s2><anchor name="utils"/>
+ trees, and should centralize parsing for those source
trees.</item></gloss><gloss><label>Expression</label><item>The base-class of
all expression objects, allowing polymorphic behaviors.</item></gloss><p>The
general architecture of the XPath module is divided into the compiler, and
categories of expression objects.</p><p><img src="xpath.gif" alt="xpath
modules"/></p><p>The most important module is the axes module. This module
implements the DOM2 <jump
href="http://www.w3.org/TR/DOM-Level-2/traversal.html#Iterator-overview";>NodeIterator</jump>
interface, and is meant to allow XPath clients to either override the default
behavior or to replace this behavior.</p><p>The <jump
href="../apidocs/org/apache/xpath/axes/LocPathIterator.html">LocPathIterator</jump>
and <jump
href="../apidocs/org/apache/xpath/axes/UnionPathIterator.html">UnionPathIterator</jump>
classes implement the <jump
href="http://www.w3.org/TR/DOM-Level-2/java-binding.html#org.w3c.dom.traversal.NodeIterator";>NodeIterator</jump>
interface, and polymorphically use <jump
href="../apidocs/org/apache/xpath/axes/AxesWalker.html">AxesWalker</jump>
derived objects to execute each step in the path. The whole trick is to
execute the <code>LocationPath</code> in depth-first document order so that
nodes can be found without necessarily looking ahead or performing a
breadth-first search. Because a document order depth-first search requires
state to be saved for many expressions, the default operations create "Waiter"
clones that have to wait while the main <code>AxesWalkers</code> traverses
child nodes (think carefully about what happens when a "//foo/baz" expression
is executed). Optimization is done by implementing specialized iterators and
<code>AxesWalkers</code> for certain types of operations. The decision as to
what type of iterator or walker will be created is done in the <jump
href="../apidocs/org/apache/xpath/axes/WalkerFactory.html">WalkerFactory</jump>
class.</p><p>[Frankly, the implementation of the default AxesWalker, with it's
waiters, is the one totally incomprehensible part of Xalan. It gets especially
difficult because you can not look to the node ahead. I would be very
interested if any rocket scientists out there can come up with a better
algorithm.]</p><anchor name="xpathdbconn"/>
+<s3 title="XPath Database Connection">
+<p>An important part of the XPath design in both Xalan 1 and Xalan 2, is to
enable database connections to be used as drivers directly to the XPath <jump
href="http://www.w3.org/TR/xpath#location-paths";>LocationPath</jump> handling.
This allows databases to be directly connected to the transform, and be able to
take advantage of internal indexing and the like. While in Xalan 1 this was
done via the <jump
href="http://xml.apache.org/xalan/apidocs/org/apache/xalan/xpath/XLocator.html";>XLocator</jump>
interface, in Xalan 2 this interface is no longer used, and has been replaced
by the DOM2 <jump
href="http://www.w3.org/TR/DOM-Level-2/traversal.html#Iterator-overview";>NodeIterator</jump>
interface. An application or extension should be able to install their own
NodeIterator for a given document.</p><p><img src="data.gif"
alt="data.gif"/></p><p>[More to do]</p></s3></s2><anchor name="utils"/>
<s2 title="Utils Package">
- <p><link>Utils Package</link></p>
<p>This package contains general utilities for use by both the xalan and
xpath packages.</p></s2><anchor name="other"/>
<s2 title="Other Packages">
- <p><link>Other Packages</link></p>
<gloss><label>client</label><item>Implementation of Xalan Applet
[should we keep this?].
</item></gloss>
- <gloss><label>lib</label><item>Implementation of Xalan-specific
extensions.</item></gloss><gloss><label>res</label><item>Contains strings that
require internationalization.</item></gloss></s2><anchor
name="compilation"/><s2 title="Xalan Stylesheet Complilation to
Java"><p><link>Xalan Stylesheet Complilation to Java</link></p><p>We are doing
some work on compiling stylesheet objects to Java. This is a work in progress,
and is not meant for general use yet. For the moment, we are writing out Java
text files, and then compiling them to bytecodes via javac, rather than
directly producing bytecodes. The CompilingStylesheetProcessor derives from
TransformerFactoryImpl to produce these classes, which are then bundled into a
jar file. For the moment the full Xalan jar is required, but we're looking at
ways to only use a subset of Xalan, so that only a minimal jar would be
required.</p><p><img src="compilation.gif"
alt="compilation.gif"/></p></s2><anchor name="optimizations"/><s2 title="Future
Optimizations"><p><link>Future Optimizations</link></p><p>This section
enumerates some optimizations that we're planning to do in future versions of
Xalan.</p><p>Likely near term optimizations (next six months?):</p><ol><li>By
pre-analysis of the stylesheet, prune nodes from the tree that have been
processed and can be predicted that they won't be visited
again.</li><li>Eliminate redundent expressions (xsl:when, variable sets, rooted
patterns, etc.).</li><li>Optimize variable patterns such as <xsl:variable
name="foo"><xsl:variable select="yada"/></xsl:variable> into
<xsl:variable name="foo" select="string(yada)"/>, in order to reduce
result tree fragment creation.</li><li>Reduce size of Stree
nodes.</li><li>Implement our own NamespaceSupport class (the SAX2 one is too
expensive).</li><li>More specialization of itterators and walkers.</li><li>Full
Java compilation support.</li><li>Schema Awareness (if "//foo", the Schema can
tell us where to look, but we need standard interface to
Schemas).</li></ol><p>Likely longer term optimizations (12-18
months?):</p><ol><li>On-the-fly indexing.</li><li>Predict if nodes won't be
processed at all, and so don't build them, achieve full streaming support for a
certain class of stylesheets.</li></ol></s2><anchor name="coding"/>
+ <gloss><label>lib</label><item>Implementation of Xalan-specific
extensions.</item></gloss><gloss><label>res</label><item>Contains strings that
require internationalization.</item></gloss></s2><anchor name="compilation"/>
+<s2 title="Xalan Stylesheet Complilation to Java">
+<p>We are doing some work on compiling stylesheet objects to Java. This is
a work in progress, and is not meant for general use yet. For the moment, we
are writing out Java text files, and then compiling them to bytecodes via
javac, rather than directly producing bytecodes. The
CompilingStylesheetProcessor derives from TransformerFactoryImpl to produce
these classes, which are then bundled into a jar file. For the moment the full
Xalan jar is required, but we're looking at ways to only use a subset of Xalan,
so that only a minimal jar would be required.</p><p><img src="compilation.gif"
alt="compilation.gif"/></p></s2><anchor name="optimizations"/>
+<s2 title="Future Optimizations">
+<p>This section enumerates some optimizations that we're planning to do in
future versions of Xalan.</p><p>Likely near term optimizations (next six
months?):</p><ol><li>By pre-analysis of the stylesheet, prune nodes from the
tree that have been processed and can be predicted that they won't be visited
again.</li><li>Eliminate redundent expressions (xsl:when, variable sets, rooted
patterns, etc.).</li><li>Optimize variable patterns such as <xsl:variable
name="foo"><xsl:variable select="yada"/></xsl:variable> into
<xsl:variable name="foo" select="string(yada)"/>, in order to reduce
result tree fragment creation.</li><li>Reduce size of Stree
nodes.</li><li>Implement our own NamespaceSupport class (the SAX2 one is too
expensive).</li><li>More specialization of itterators and walkers.</li><li>Full
Java compilation support.</li><li>Schema Awareness (if "//foo", the Schema can
tell us where to look, but we need standard interface to
Schemas).</li></ol><p>Likely longer term optimizations (12-18
months?):</p><ol><li>On-the-fly indexing.</li><li>Predict if nodes won't be
processed at all, and so don't build them, achieve full streaming support for a
certain class of stylesheets.</li></ol></s2><anchor name="coding"/>
<s2 title="Coding Conventions">
- <p><link>Coding Conventions</link></p>
<p>This section documents the coding conventions used in the Xalan
source.</p>
<ol>
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