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Posted to commits@xalan.apache.org by sb...@apache.org on 2001/01/12 08:46:58 UTC
cvs commit: xml-xalan/java/xdocs/sources/design compilation.gif xalan.gif xslt_abstract.gif design2_0_0.xml trax.gif xalan1_1x1.gif
sboag 01/01/11 23:46:58
Modified: java/xdocs/sources/design design2_0_0.xml trax.gif
xalan1_1x1.gif
Added: java/xdocs/sources/design compilation.gif xalan.gif
xslt_abstract.gif
Log:
Update of design doc to match reality.
Revision Changes Path
1.3 +63 -314 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 1.2
retrieving revision 1.3
diff -u -r1.2 -r1.3
--- design2_0_0.xml 2001/01/10 20:48:27 1.2
+++ design2_0_0.xml 2001/01/12 07:46:58 1.3
@@ -5,7 +5,8 @@
<p>Author: Scott Boag<br/>State: In Progress</p>
<ul>
<li><link anchor="intro">Introduction</link></li>
- <li><link anchor="overarch">Overview of Architecture</link></li>
+ <li><link anchor="requirements">Xalan Requirements</link></li>
+ <li><link anchor="overarch">Overview of Architecture</link></li>
<li><link anchor="process">Process Module</link></li>
<li><link anchor="templates">Templates Module</link></li>
<li><link anchor="transformer">Transformer Module</link></li>
@@ -17,26 +18,25 @@
<ul><li><link anchor="xpathdbconn">XPath Database Connection</link></li></ul>
<li><link anchor="utils">Utils Package</link></li>
<li><link anchor="other">Other Packages</link></li>
- <li><link anchor="coding">Coding Conventions</link></li>
- <li><link anchor="open">Open Issues</link></li>
+ <li><link anchor="compilation">Xalan Stylesheet Complilation to Java</link></li><li><link anchor="optimizations">Future Optimizations</link></li><li><link anchor="coding">Coding Conventions</link></li>
+
<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. The main goals of this redesign are
- to: </p>
- <ol>
+ 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>
+ <p>The main goals of this redesign are
+ to: </p><ol>
<li>Make the design and code more understandable by Open Source
people.</li>
<li>Reduce code size and complexity.</li>
<li>By simplifying the code, make optimization easier.</li>
<li>Make modules generally more localized, and less tangled with other
modules.</li>
- <li>Begin the adoption of the TrAX (Transformations for XML)
- interfaces.</li>
- <li>Increase the streamability of transformations.</li></ol>
+ <li>Conform to the <jump href="http://java.sun.com/aboutJava/communityprocess/jsr/jsr_063_jaxp11.html">javax.xml.transform (TrAX [Transformations for XML])</jump> interfaces.</li>
+ <li>Increase the ability to incrementally produce the result tree.</li></ol>
<p>The techniques used toward these goals are to:</p>
<ol>
<li>In general, flatten the hierarchy of packages, in order to make the
@@ -59,13 +59,21 @@
expect that the code will be faster once this work is complete.</li>
</ol>
<p>How well we've achieved the goals will be measured by feedback from the
- <jump href="http://xml-archive.webweaving.org/xml-archive-xalan">Xalan-dev</jump> list, and by software metrics tools.</p>
+ <jump href="http://archive.covalent.net/">Xalan-dev</jump> list, and by software metrics tools.</p>
<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="overarch"/>
+ </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="Overview of Architecture">
- <p><link>Overview of Architecture</link></p>
- <p>Xalan 2.0 is divided into four major modules, and various smaller
+ <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><p>The term "tree", 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><p><img src="xslt_abstract.gif" alt="xslt_abstract.gif"/></p><p>The primary interface for Xalan 2.0 external usage is defined in the <jump href="../apidocs/javax/xml/transform/package-summary.html#package_description">javax.xml.transform</jump> interfaces. These interfaces define a standard and powerful interface to perform tree-based transformations.</p>
+ <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>
@@ -89,7 +97,7 @@
patterns.</item>
</gloss>
<p>In addition to the above modules, Xalan implements the
- <jump href="http://trax.openxml.org/">TrAX</jump> interfaces, and depends on the
+ <jump href="../apidocs/javax/xml/transform/package-summary.html#package_description">javax.xml.transform</jump> interfaces, and depends on the
<jump href="http://www.megginson.com/SAX/Java/index.html">SAX2</jump> and <jump href="http://www.w3.org/TR/DOM-Level-2/">DOM</jump> packages.
</p><p><img src="trax.gif" alt="trax.gif"/></p><p>There is also a general utilities package that contains both XML utility
classes such as QName, but generally useful classes such as
@@ -121,6 +129,7 @@
<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>
<item>This package contains classes and interfaces that allow a caller to
@@ -129,60 +138,58 @@
</gloss>
<gloss>
<label><code><jump href="../apidocs/org/apache/xalan/xslt/package-summary.html">org.apache.xalan.xslt</jump></code></label>
- <item>This package is for backwards compatibility with applications that
- depend on Xalan 1.x interfaces.</item>
+ <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>Process Module</link></p>
- <p>The <code>org.apache.xalan.process</code> module implements the
- <code>org.apache.xalan.trax.Processor</code> interface, which provides a
+ <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
factory method for creating a concrete Processor instance, and provides methods
- for creating a <code>org.apache.xalan.trax.Templates</code> instance, which, in
+ for creating a <code><jump href="../apidocs/javax/xml/transform/Templates.html">javax.xml.transform.Templates</jump></code> 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>
- <p>The overall strategy is to define a schema that dictates the legal
+ <p>The overall strategy is to define a schema in that dictates the legal
structure for XSLT elements and attributes, and to associate with those
elements construction-time processors that can fill in the appropriate fields
in the top-level Stylesheet object, and also associate classes in the templates
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>org.apache.xalan.processor.XSLTSchema</code>, and it is here that the
+ <code><jump href="../apidocs/org/apache/xalan/processor/XSLTSchema.html">org.apache.xalan.processor.XSLTSchema</jump></code>, and it is here that the
XSLT schema structure is defined. XSLTSchema uses
- <code>org.apache.xalan.processor.XSLTElementDef</code> to define elements, and
- <code>org.apache.xalan.processor.XSLTAttributeDef</code> to define attributes.
+ <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.
Both classes hold the allowed namespace, local name, and type of element or
attribute. The XSLTElementDef also holds a reference to a
- <code>org.apache.xalan.processor.XSLTElementProcessor</code>, and a sometimes a
+ <code><jump href="../apidocs/org/apache/xalan/processor/XSLTElementProcessor.html">org.apache.xalan.processor.XSLTElementProcessor</jump></code>, and a sometimes a
<code>Class</code> object, with which it can create objects that derive from
- <code>org.apache.xalan.templates.ElemTemplateElement</code>. In addition, the
+ <code><jump href="../apidocs/org/apache/xalan/templates/ElemTemplateElement.html">org.apache.xalan.templates.ElemTemplateElement</jump></code>. 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>org.apache.xalan.trax.Processor</code>
- interface is in <code>org.apache.xalan.processor.StylesheetProcessor</code>,
- which creates a <code>org.apache.xalan.processor.StylesheetHandler</code>
+ <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>
instance. This instance acts as the ContentHandler for the parse events, and is
- handed to the <code>org.xml.sax.XMLReader</code>, which the StylesheetProcessor
- uses to parse the XSLT document. The StylesheetHandler then receives the parse
+ handed to the <code><jump href="../apidocs/org/xml/sax/XMLReader.html">org.xml.sax.XMLReader</jump></code>, 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 XSLTElementProcessor for the given event, as dictated by the
- XSLTElementDef that is associated with the given event.</p>
- <p><img src="process.gif" alt="process.gif"/></p>
- </s2><anchor name="templates"/>
+ 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>org.apache.xalan.templates</code> module implements the
- <code>org.apache.xalan.trax.Templates</code> interface, and defines a set of
+ <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
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>A <code>StylesheetRoot</code>, which implements the
- <code>Templates</code> interface, is a type of <code>StylesheetComposed</code>,
- which is a <code>Stylesheet</code> composed of itself and all included
+ <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
<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
@@ -199,265 +206,27 @@
<code>StylesheetComposed</code> derivative object, if it is a root
<code>Stylesheet</code> or imported <code>Stylesheet</code>, has "composed"
getter methods that do take into account imported and included stylesheets, for
- some of these properties. The table of Stylesheet properties, with composed
- methods, is as follows. Note that the names of the attributes are according to
- a formula for translating the xsl names to the Java get/set method names.</p>
- <table>
- <tr>
- <th>Property</th>
- <th>Type</th>
- <th>XSL Origin</th>
- <th>Composed Methods</th>
- <th>Note</th>
- </tr>
- <tr>
- <td>XmlnsXsl</td>
- <td>String</td>
- <td>xmlns:xsl</td>
- <td>(none, applies to stylesheet only)</td>
- <td></td>
- </tr>
- <tr>
- <td>ExtensionElementPrefixes</td>
- <td>StringVector</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#extension-element">extension-element-prefixes</jump></code>
- attribute</td>
- <td>(none, applies to stylesheet only)</td>
- <td></td>
- </tr>
- <tr>
- <td>ExcludeResultPrefixes</td>
- <td>StringVector</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#literal-result-element">exclude-result-prefixes
- or xsl:exclude-result-prefixes</jump></code> attributes</td>
- <td>(not sure about this... only from root?)</td>
- <td>I think this should be a root method, and a single list should be
- made, like with xsl:output.</td>
- </tr>
- <tr>
- <td>Id</td>
- <td>String</td>
- <td>The <code><jump href="http://www.w3.org/TR/xslt#section-Embedding-Stylesheets">id</jump></code>
- attribute</td>
- <td>(none, applies to stylesheet only)</td>
- <td></td>
- </tr>
- <tr>
- <td>Version</td>
- <td>String</td>
- <td>The <code><jump href="http://www.w3.org/TR/xslt#forwards">version</jump></code> attribute</td>
- <td>(none, applies to stylesheet only)</td>
- <td></td>
- </tr>
- <tr>
- <td>XmlSpace</td>
- <td>boolean</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#strip">xml:space</jump></code> attribute</td>
- <td>(none, applies to stylesheet only)</td>
- <td></td>
- </tr>
- <tr>
- <td>Import</td>
- <td>Vector (list of StylesheetComposed objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#import">xsl:import</jump></code> element</td>
- <td>getImportComposed(int i) / getImportCountComposed()</td>
- <td>Composed list contains all imported sheets, not the importing sheet
- itself.</td>
- </tr>
- <tr>
- <td>Include</td>
- <td>Vector (list of Stylesheet objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#include">xsl:include</jump></code> element</td>
-
- <td>getIncludeComposed(int i) / getIncludeCountComposed()</td>
- <td>Composed list contains all directly or indirectly included
- stylesheets.</td>
- </tr>
- <tr>
- <td>DecimalFormat</td>
- <td>Stack (list of DecimalFormatProperties objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#format-number">xsl:decimal-format</jump></code>
- element</td>
- <td>getDecimalFormatComposed(QName name)</td>
- <td></td>
- </tr>
- <tr>
- <td>StripSpaces</td>
- <td>Stack (list of XPath match pattern objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#strip">xsl:strip-space</jump></code>
- element</td>
- <td>getWhiteSpaceInfo(TransformerImpl transformContext, Node
- sourceTree, Element targetElement)</td>
- <td></td>
- </tr>
- <tr>
- <td>PreserveSpaces</td>
- <td>Stack (list of XPath match pattern objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#strip">xsl:preserve-space</jump></code>
- element</td>
- <td>getWhiteSpaceInfo(TransformerImpl transformContext, Node
- sourceTree, Element targetElement)</td>
- <td></td>
- </tr>
- <tr>
- <td>Output</td>
- <td>OutputFormatExtended</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#output">xsl:output</jump></code> element</td>
- <td>getOutputComposed() on StylesheetRoot only</td>
- <td></td>
- </tr>
- <tr>
- <td>Key</td>
- <td>Vector (list of KeyDeclaration objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#key">xsl:key</jump></code> element</td>
- <td>getKeysComposed()</td>
- <td></td>
- </tr>
- <tr>
- <td>AttributeSet</td>
- <td>Vector (list of ElemAttributeSet objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#attribute-sets">xsl:attribute-set</jump></code>
- element</td>
- <td>On StylesheetRoot only?</td>
- <td></td>
- </tr>
- <tr>
- <td>Variable</td>
- <td>Vector (list of ElemVariable objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#top-level-variables">xsl:variable</jump></code>
- element</td>
- <td></td>
- <td></td>
- </tr>
- <tr>
- <td>Param</td>
- <td>Vector (list of ElemParam objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#top-level-variables">xsl:param</jump></code>
- element</td>
- <td></td>
- <td></td>
- </tr>
- <tr>
- <td>Template</td>
- <td>Vector (list of ElemTemplate objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#section-Defining-Template-Rules">xsl:template</jump></code>
- element</td>
- <td>getTemplateComposed(TransformerImpl transformContext, Node
- sourceTree, Node targetNode, QName mode) and getTemplateComposed(QName
- qname)</td>
- <td></td>
- </tr>
- <tr>
- <td>NamespaceAlias</td>
- <td>Vector (list of ElemTemplate objects)</td>
- <td><code><jump href="http://www.w3.org/TR/xslt#literal-result-element">xsl:namespace-alias</jump></code>
- element</td>
- <td>On StylesheetRoot only?</td>
- <td></td>
- </tr>
- <tr>
- <td>NonXslTopLevel</td>
- <td>Hashtable (table of opaque objects keyed by QName)</td>
- <td>Any top-level non-xslt element.</td>
- <td>none.</td>
- <td></td>
- </tr>
- <tr>
- <td>Href</td>
- <td>URL</td>
- <td>The location of the stylesheet, possibly set by xsl:include or
- xsl:import.</td>
- <td>none.</td>
- <td></td>
- </tr>
- <tr>
- <td>StylesheetRoot</td>
- <td>StylesheetRoot</td>
- <td>The root of the stylesheet tree, for quick access.</td>
- <td>none.</td>
- <td></td>
- </tr>
- <tr>
- <td>StylesheetParent</td>
- <td>Stylesheet</td>
- <td>The importing or including stylesheet.</td>
- <td>none.</td>
- <td></td>
- </tr>
- <tr>
- <td>StylesheetComposed</td>
- <td>StylesheetComposed</td>
- <td>The closest importing stylesheet.</td>
- <td>none.</td>
- <td></td>
- </tr>
- <tr>
- <td>NamespaceDecls</td>
- <td>Linked list of NameSpace elements</td>
- <td>xmlns:foo attribute map</td>
- <td>(none, applies to stylesheet only)</td>
- <td></td>
- </tr>
- </table>
+ some of these properties.</p>
+
</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="http://trax.openxml.org/javadoc/trax/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), 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 Serializer), and the Transformer. For one thing,
+ <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
+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 Counter 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 <code><jump href="../apidocs/org/apache/xalan/transformer/Counter.html">Counter</jump></code> 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 CountersTable class is a table of counters, keyed by ElemNumber objects, each
- of which has a list of Counter objects.</item></gloss><gloss><label>KeyIterator, KeyManager, and KeyTable</label><item>These classes handle mapping of keys declared with the xsl:key element.</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
+ 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
+ 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 org.apache.xalan 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 a streaming 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 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.</p><p>This kind of streaming 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><p>Vincent-Olivier Arsenault <vincent@neuro6.com> has proposed the following design:</p><p>By looking at the stylesheet you know how streamable it is (of course this
-needs strict adherence to the xslt recommendation). since there's a root
-template and no <xsl:apply-templates/> you can build your context list
-containing only absolute xpath which means nodes get out of context
-faster).</p>
-
-<p>The paths of the relevant nodes, for this stylesheet, are (ok this is an
-example, so I may be missing some):</p>
-<ol>
-<li>path: "/address" context: "address" (at </address>, you get rid of the
-whole "person/address" stuff);</li>
-
-<li>path: "/adn" context: "adn";</li>
-
-<li>path: "/medicalrecord" context: "/" (for possibly repetitive nodes, the
-context is always the parent node).</li>
-</ol>
-<p>And all the rest goes to trash!!!!</p>
-
-<p>Let me refine:</p>
-
-<p>you analyze the whole stylesheet like that (would be good if optimization
-and xpath list could be done simultaneously) and you end up with a list of
-expanded paths mapped to all the templates.</p>
+ 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>.
-<p>An entry in the list (i would call this list the transformation stack) would
-consist of 4 things:</p>
-<ol>
-<li>the relevance context xpath (on which the input nodes will be tested for
-pertinence: do we keep it of not);</li>
-
-<li>the transformation rule to apply to the matching nodes (this can just be a
-forwarder to another template transformation stack);</li>
-
-<li>a result buffer (in which the nodes that can't be streamed are temporarily
-stored);</li>
-
-<li>the streaming context xpath (triggers streaming of the buffer to the
-output).</li>
-</ol><anchor name="extensions"/>
-</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>.
-
-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 1 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"/>
+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>
@@ -466,23 +235,18 @@
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 LocPathIterator and UnionPathIterator 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 AxesWalker derived objects to execute each step in the path. The whole trick is to execute the LocationPath in depth-first document order so that nodes can be found without necessarily looking ahead or performing a breadth-first search.</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 <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"/>
<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. It is the intention that many of these utility classes (or their equivalents) be eventually brought into the org.apache.xml package for general use. The list of major utilities are as follows:</p><gloss><label>AttList</label><item>Wraps a DOM attribute list in a SAX Attributes.</item></gloss><gloss><label>BoolStack, IntStack, IntVector, etc.</label><item>Simple stacks and vectors for primitive values.</item></gloss><gloss><label>DefaultErrorHandler</label><item>Implements SAX error handler for default reporting.</item></gloss><gloss><label>DOMBuilder</label><item>Takes SAX events (in addition to some extra events
- that SAX doesn't handle yet) and adds the result to a document
- or document fragment.</item></gloss><gloss><label>Heap</label><item>Classic heap implementation.</item></gloss><gloss><label>MutableAttrListImpl</label><item>Mutable version of AttributesImpl.</item></gloss><gloss><label>NameSpace</label><item>A representation of a namespace.</item></gloss><gloss><label>NodeVector</label><item>A very simple table that stores a list of Nodes.</item></gloss><gloss><label>ObjectPool</label><item>Used for reuse of objects.</item></gloss><gloss><label>PrefixResolver</label><item>The class that implements this interface can resolve prefixes
- to namespaces.</item></gloss><gloss><label>PrefixResolverDefault</label><item>This class implements a generic PrefixResolver for a DOM, that
- can be used to perform prefix-to-namespace lookup
- for an XPath.</item></gloss><gloss><label>QName</label><item>Class to represent a qualified XML name.</item></gloss><gloss><label>StringToStringTable</label><item>A very simple lookup table that stores a list of strings for lookup. Used when a hashtable is too much overhead.</item></gloss><gloss><label>SystemIDResolver</label><item>Able to take a SystemID string and try and turn it into a good absolute URL.</item></gloss><gloss><label>TreeWalker</label><item>Implements a Visitor design pattern, doing a pre-order walk of the DOM tree, calling a ContentHandler interface as it goes. Used for DOM-to-SAX conversion.</item></gloss><gloss><label>Trie</label><item>A digital search trie for 7-bit ASCII text.</item></gloss><gloss><label>UnImplNode</label><item>To be subclassed by classes that wish to act as DOM nodes, without having to implement all the methods. Widely used.</item></gloss></s2><anchor name="other"/>
+ <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>dtm</label><item>Implementation of the Document Table Model (DTM) [Should we keep this?].</item></gloss>
- <gloss><label>extensions</label><item>Implementation of Xalan Extension Mechanism, which uses the Bean Scripting Framework.</item></gloss>
- <gloss><label>lib</label><item>Implementation of Xalan-specific extensions [I want to add lots more extensions to this package!].</item></gloss><gloss><label>res</label><item>Contains strings that require internationalization.</item></gloss></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><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"/>
<s2 title="Coding Conventions">
<p><link>Coding Conventions</link></p>
<p>This section documents the coding conventions used in the Xalan
@@ -504,20 +268,5 @@
protected member variables should not be declared.</li>
</ol>
</s2><anchor name="open"/>
- <s2 title="Open Issues">
- <p><link>Open Issues</link></p>
- <p>This section documents architectural and design issues that I still
- consider to be open or unsolved. (This list is ongoing, and will change over
- time... it's simply a place for me to note problems that are ongoing and need
- to be solved.)</p>
- <gloss>
- <label>Space stripping</label>
- <item>In Xalan 1.x, it is clear that space stripping was a major
- performance issue. This needs to be solved in Xalan 2.0 by stripping the
- space nodes as the document is being parsed. This is a major problem though for
- DOM trees. This can be perhaps be solved by preprocessing the DOM tree and
- creating a table of space-stripping parent elements, when the nodes can't be
- pre-stripped.</item>
- </gloss>
- </s2>
+
</s1>
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