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Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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Daniel Veillard7a2c2ee2004-08-14 13:56:39 +0000[diff] [blame]10</style><title>Catalog support</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo" /></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo" /></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo" /></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"><h1>The XML C parser and toolkit of Gnome</h1><h2>Catalog support</h2></td></tr></table></td></tr></table></td></tr></table><table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html">Home</a></li><li><a href="intro.html">Introduction</a></li><li><a href="FAQ.html">FAQ</a></li><li><a href="docs.html" style="font-weight:bold">Developer Menu</a></li><li><a href="bugs.html">Reporting bugs and getting help</a></li><li><a href="help.html">How to help</a></li><li><a href="downloads.html">Downloads</a></li><li><a href="news.html">News</a></li><li><a href="XMLinfo.html">XML</a></li><li><a href="XSLT.html">XSLT</a></li><li><a href="xmldtd.html">Validation &amp; DTDs</a></li><li><a href="encoding.html">Encodings support</a></li><li><a href="catalog.html">Catalog support</a></li><li><a href="namespaces.html">Namespaces</a></li><li><a href="contribs.html">Contributions</a></li><li><a href="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a href="html/index.html" style="font-weight:bold">API Menu</a></li><li><a href="guidelines.html">XML Guidelines</a></li><li><a href="ChangeLog.html">ChangeLog</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li><li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li><li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li><li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li><li><a href="ftp://xmlsoft.org/">FTP</a></li><li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li><li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li><li><a href="http://www.zveno.com/open_source/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li><li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>Table of Content:</p><ol><li><a href="General2">General overview</a></li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]11 <li><a href="#definition">The definition</a></li>
12 <li><a href="#Simple">Using catalogs</a></li>
13 <li><a href="#Some">Some examples</a></li>
14 <li><a href="#reference">How to tune catalog usage</a></li>
15 <li><a href="#validate">How to debug catalog processing</a></li>
16 <li><a href="#Declaring">How to create and maintain catalogs</a></li>
17 <li><a href="#implemento">The implementor corner quick review of the
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]18 API</a></li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]19 <li><a href="#Other">Other resources</a></li>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]20</ol><h3><a name="General2" id="General2">General overview</a></h3><p>What is a catalog? Basically it's a lookup mechanism used when an entity
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]21(a file or a remote resource) references another entity. The catalog lookup
22is inserted between the moment the reference is recognized by the software
23(XML parser, stylesheet processing, or even images referenced for inclusion
24in a rendering) and the time where loading that resource is actually
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]25started.</p><p>It is basically used for 3 things:</p><ul><li>mapping from "logical" names, the public identifiers and a more
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]26 concrete name usable for download (and URI). For example it can associate
Daniel Veillardffb120d2001-08-23 00:52:23 +0000[diff] [blame]27 the logical name
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]28 <p>"-//OASIS//DTD DocBook XML V4.1.2//EN"</p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]29 <p>of the DocBook 4.1.2 XML DTD with the actual URL where it can be
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]30 downloaded</p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]31 <p>http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd</p>
32 </li>
33 <li>remapping from a given URL to another one, like an HTTP indirection
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]34 saying that
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]35 <p>"http://www.oasis-open.org/committes/tr.xsl"</p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]36 <p>should really be looked at</p>
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]37 <p>"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"</p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]38 </li>
39 <li>providing a local cache mechanism allowing to load the entities
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]40 associated to public identifiers or remote resources, this is a really
41 important feature for any significant deployment of XML or SGML since it
MDT 2001 John Fleck04685002001-09-03 16:11:47 +0000[diff] [blame]42 allows to avoid the aleas and delays associated to fetching remote
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]43 resources.</li>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]44</ul><h3><a name="definition" id="definition">The definitions</a></h3><p>Libxml, as of 2.4.3 implements 2 kind of catalogs:</p><ul><li>the older SGML catalogs, the official spec is SGML Open Technical
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]45 Resolution TR9401:1997, but is better understood by reading <a href="http://www.jclark.com/sp/catalog.htm">the SP Catalog page</a> from
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]46 James Clark. This is relatively old and not the preferred mode of
47 operation of libxml.</li>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]48 <li><a href="http://www.oasis-open.org/committees/entity/spec.html">XML
Daniel Veillardaf43f632002-03-08 15:05:20 +0000[diff] [blame]49 Catalogs</a> is far more flexible, more recent, uses an XML syntax and
50 should scale quite better. This is the default option of libxml.</li>
Daniel Veillard8a469172003-06-12 16:05:07 +0000[diff] [blame]51</ul><p></p><h3><a name="Simple" id="Simple">Using catalog</a></h3><p>In a normal environment libxml2 will by default check the presence of a
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]52catalog in /etc/xml/catalog, and assuming it has been correctly populated,
53the processing is completely transparent to the document user. To take a
54concrete example, suppose you are authoring a DocBook document, this one
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]55starts with the following DOCTYPE definition:</p><pre>&lt;?xml version='1.0'?&gt;
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]56&lt;!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN"
57 "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd"&gt;</pre><p>When validating the document with libxml, the catalog will be
58automatically consulted to lookup the public identifier "-//Norman Walsh//DTD
59DocBk XML V3.1.4//EN" and the system identifier
60"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd", and if these entities have
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]61been installed on your system and the catalogs actually point to them, libxml
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]62will fetch them from the local disk.</p><p style="font-size: 10pt"><strong>Note</strong>: Really don't use this
Daniel Veillard8a469172003-06-12 16:05:07 +0000[diff] [blame]63DOCTYPE example it's a really old version, but is fine as an example.</p><p>Libxml2 will check the catalog each time that it is requested to load an
MDT 2001 John Fleck04685002001-09-03 16:11:47 +0000[diff] [blame]64entity, this includes DTD, external parsed entities, stylesheets, etc ... If
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]65your system is correctly configured all the authoring phase and processing
MDT 2001 John Fleck04685002001-09-03 16:11:47 +0000[diff] [blame]66should use only local files, even if your document stays portable because it
Daniel Veillard8a469172003-06-12 16:05:07 +0000[diff] [blame]67uses the canonical public and system ID, referencing the remote document.</p><h3><a name="Some" id="Some">Some examples:</a></h3><p>Here is a couple of fragments from XML Catalogs used in libxml2 early
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]68regression tests in <code>test/catalogs</code> :</p><pre>&lt;?xml version="1.0"?&gt;
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]69&lt;!DOCTYPE catalog PUBLIC
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]70 "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
71 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"&gt;
72&lt;catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"&gt;
73 &lt;public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
74 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/&gt;
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]75...</pre><p>This is the beginning of a catalog for DocBook 4.1.2, XML Catalogs are
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]76written in XML, there is a specific namespace for catalog elements
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]77"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry in this
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]78catalog is a <code>public</code> mapping it allows to associate a Public
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]79Identifier with an URI.</p><pre>...
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]80 &lt;rewriteSystem systemIdStartString="http://www.oasis-open.org/docbook/"
81 rewritePrefix="file:///usr/share/xml/docbook/"/&gt;
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]82...</pre><p>A <code>rewriteSystem</code> is a very powerful instruction, it says that
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]83any URI starting with a given prefix should be looked at another URI
84constructed by replacing the prefix with an new one. In effect this acts like
85a cache system for a full area of the Web. In practice it is extremely useful
86with a file prefix if you have installed a copy of those resources on your
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]87local system.</p><pre>...
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]88&lt;delegatePublic publicIdStartString="-//OASIS//DTD XML Catalog //"
89 catalog="file:///usr/share/xml/docbook.xml"/&gt;
90&lt;delegatePublic publicIdStartString="-//OASIS//ENTITIES DocBook XML"
91 catalog="file:///usr/share/xml/docbook.xml"/&gt;
92&lt;delegatePublic publicIdStartString="-//OASIS//DTD DocBook XML"
93 catalog="file:///usr/share/xml/docbook.xml"/&gt;
94&lt;delegateSystem systemIdStartString="http://www.oasis-open.org/docbook/"
95 catalog="file:///usr/share/xml/docbook.xml"/&gt;
96&lt;delegateURI uriStartString="http://www.oasis-open.org/docbook/"
97 catalog="file:///usr/share/xml/docbook.xml"/&gt;
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]98...</pre><p>Delegation is the core features which allows to build a tree of catalogs,
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]99easier to maintain than a single catalog, based on Public Identifier, System
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]100Identifier or URI prefixes it instructs the catalog software to look up
101entries in another resource. This feature allow to build hierarchies of
102catalogs, the set of entries presented should be sufficient to redirect the
103resolution of all DocBook references to the specific catalog in
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]104<code>/usr/share/xml/docbook.xml</code> this one in turn could delegate all
105references for DocBook 4.2.1 to a specific catalog installed at the same time
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]106as the DocBook resources on the local machine.</p><h3><a name="reference" id="reference">How to tune catalog usage:</a></h3><p>The user can change the default catalog behaviour by redirecting queries
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]107to its own set of catalogs, this can be done by setting the
108<code>XML_CATALOG_FILES</code> environment variable to a list of catalogs, an
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]109empty one should deactivate loading the default <code>/etc/xml/catalog</code>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]110default catalog</p><h3><a name="validate" id="validate">How to debug catalog processing:</a></h3><p>Setting up the <code>XML_DEBUG_CATALOG</code> environment variable will
Daniel Veillard8a469172003-06-12 16:05:07 +0000[diff] [blame]111make libxml2 output debugging informations for each catalog operations, for
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]112example:</p><pre>orchis:~/XML -&gt; xmllint --memory --noout test/ent2
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]113warning: failed to load external entity "title.xml"
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]114orchis:~/XML -&gt; export XML_DEBUG_CATALOG=
115orchis:~/XML -&gt; xmllint --memory --noout test/ent2
116Failed to parse catalog /etc/xml/catalog
117Failed to parse catalog /etc/xml/catalog
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]118warning: failed to load external entity "title.xml"
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]119Catalogs cleanup
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]120orchis:~/XML -&gt; </pre><p>The test/ent2 references an entity, running the parser from memory makes
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]121the base URI unavailable and the the "title.xml" entity cannot be loaded.
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]122Setting up the debug environment variable allows to detect that an attempt is
123made to load the <code>/etc/xml/catalog</code> but since it's not present the
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]124resolution fails.</p><p>But the most advanced way to debug XML catalog processing is to use the
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]125<strong>xmlcatalog</strong> command shipped with libxml2, it allows to load
126catalogs and make resolution queries to see what is going on. This is also
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]127used for the regression tests:</p><pre>orchis:~/XML -&gt; ./xmlcatalog test/catalogs/docbook.xml \
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]128 "-//OASIS//DTD DocBook XML V4.1.2//EN"
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]129http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]130orchis:~/XML -&gt; </pre><p>For debugging what is going on, adding one -v flags increase the verbosity
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]131level to indicate the processing done (adding a second flag also indicate
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]132what elements are recognized at parsing):</p><pre>orchis:~/XML -&gt; ./xmlcatalog -v test/catalogs/docbook.xml \
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]133 "-//OASIS//DTD DocBook XML V4.1.2//EN"
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]134Parsing catalog test/catalogs/docbook.xml's content
135Found public match -//OASIS//DTD DocBook XML V4.1.2//EN
136http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
137Catalogs cleanup
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]138orchis:~/XML -&gt; </pre><p>A shell interface is also available to debug and process multiple queries
139(and for regression tests):</p><pre>orchis:~/XML -&gt; ./xmlcatalog -shell test/catalogs/docbook.xml \
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]140 "-//OASIS//DTD DocBook XML V4.1.2//EN"
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]141&gt; help
142Commands available:
143public PublicID: make a PUBLIC identifier lookup
144system SystemID: make a SYSTEM identifier lookup
145resolve PublicID SystemID: do a full resolver lookup
146add 'type' 'orig' 'replace' : add an entry
147del 'values' : remove values
148dump: print the current catalog state
149debug: increase the verbosity level
150quiet: decrease the verbosity level
151exit: quit the shell
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]152&gt; public "-//OASIS//DTD DocBook XML V4.1.2//EN"
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]153http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
154&gt; quit
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]155orchis:~/XML -&gt; </pre><p>This should be sufficient for most debugging purpose, this was actually
156used heavily to debug the XML Catalog implementation itself.</p><h3><a name="Declaring" id="Declaring">How to create and maintain</a> catalogs:</h3><p>Basically XML Catalogs are XML files, you can either use XML tools to
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]157manage them or use <strong>xmlcatalog</strong> for this. The basic step is
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]158to create a catalog the -create option provide this facility:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --create tst.xml
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]159&lt;?xml version="1.0"?&gt;
160&lt;!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
161 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"&gt;
162&lt;catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/&gt;
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]163orchis:~/XML -&gt; </pre><p>By default xmlcatalog does not overwrite the original catalog and save the
MDT 2001 John Fleck04685002001-09-03 16:11:47 +0000[diff] [blame]164result on the standard output, this can be overridden using the -noout
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]165option. The <code>-add</code> command allows to add entries in the
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]166catalog:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --noout --create --add "public" \
167 "-//OASIS//DTD DocBook XML V4.1.2//EN" \
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]168 http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd tst.xml
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]169orchis:~/XML -&gt; cat tst.xml
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]170&lt;?xml version="1.0"?&gt;
171&lt;!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" \
172 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"&gt;
173&lt;catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"&gt;
174&lt;public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
175 uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/&gt;
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]176&lt;/catalog&gt;
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]177orchis:~/XML -&gt; </pre><p>The <code>-add</code> option will always take 3 parameters even if some of
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]178the XML Catalog constructs (like nextCatalog) will have only a single
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]179argument, just pass a third empty string, it will be ignored.</p><p>Similarly the <code>-del</code> option remove matching entries from the
180catalog:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --del \
Daniel Veillard024f1992003-12-10 16:43:49 +0000[diff] [blame]181 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" tst.xml
182&lt;?xml version="1.0"?&gt;
183&lt;!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
184 "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"&gt;
185&lt;catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/&gt;
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]186orchis:~/XML -&gt; </pre><p>The catalog is now empty. Note that the matching of <code>-del</code> is
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]187exact and would have worked in a similar fashion with the Public ID
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]188string.</p><p>This is rudimentary but should be sufficient to manage a not too complex
189catalog tree of resources.</p><h3><a name="implemento" id="implemento">The implementor corner quick review of the
190API:</a></h3><p>First, and like for every other module of libxml, there is an
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]191automatically generated <a href="html/libxml-catalog.html">API page for
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]192catalog support</a>.</p><p>The header for the catalog interfaces should be included as:</p><pre>#include &lt;libxml/catalog.h&gt;</pre><p>The API is voluntarily kept very simple. First it is not obvious that
Daniel Veillardffb120d2001-08-23 00:52:23 +0000[diff] [blame]193applications really need access to it since it is the default behaviour of
Daniel Veillard95c09d92003-07-07 12:11:06 +0000[diff] [blame]194libxml2 (Note: it is possible to completely override libxml2 default catalog
195by using <a href="html/libxml-parser.html">xmlSetExternalEntityLoader</a> to
Daniel Veillard8a469172003-06-12 16:05:07 +0000[diff] [blame]196plug an application specific resolver).</p><p>Basically libxml2 support 2 catalog lists:</p><ul><li>the default one, global shared by all the application</li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]197 <li>a per-document catalog, this one is built if the document uses the
Daniel Veillardffb120d2001-08-23 00:52:23 +0000[diff] [blame]198 <code>oasis-xml-catalog</code> PIs to specify its own catalog list, it is
199 associated to the parser context and destroyed when the parsing context
200 is destroyed.</li>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]201</ul><p>the document one will be used first if it exists.</p><h4>Initialization routines:</h4><p>xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs() should be
Daniel Veillardffb120d2001-08-23 00:52:23 +0000[diff] [blame]202used at startup to initialize the catalog, if the catalog should be
203initialized with specific values xmlLoadCatalog() or xmlLoadCatalogs()
204should be called before xmlInitializeCatalog() which would otherwise do a
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]205default initialization first.</p><p>The xmlCatalogAddLocal() call is used by the parser to grow the document
206own catalog list if needed.</p><h4>Preferences setup:</h4><p>The XML Catalog spec requires the possibility to select default
Daniel Veillardffb120d2001-08-23 00:52:23 +0000[diff] [blame]207preferences between public and system delegation,
208xmlCatalogSetDefaultPrefer() allows this, xmlCatalogSetDefaults() and
209xmlCatalogGetDefaults() allow to control if XML Catalogs resolution should
210be forbidden, allowed for global catalog, for document catalog or both, the
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]211default is to allow both.</p><p>And of course xmlCatalogSetDebug() allows to generate debug messages
212(through the xmlGenericError() mechanism).</p><h4>Querying routines:</h4><p>xmlCatalogResolve(), xmlCatalogResolveSystem(), xmlCatalogResolvePublic()
Daniel Veillardffb120d2001-08-23 00:52:23 +0000[diff] [blame]213and xmlCatalogResolveURI() are relatively explicit if you read the XML
214Catalog specification they correspond to section 7 algorithms, they should
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]215also work if you have loaded an SGML catalog with a simplified semantic.</p><p>xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the same but
216operate on the document catalog list</p><h4>Cleanup and Miscellaneous:</h4><p>xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal() is
217the per-document equivalent.</p><p>xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically modify the
Daniel Veillardffb120d2001-08-23 00:52:23 +0000[diff] [blame]218first catalog in the global list, and xmlCatalogDump() allows to dump a
219catalog state, those routines are primarily designed for xmlcatalog, I'm not
220sure that exposing more complex interfaces (like navigation ones) would be
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]221really useful.</p><p>The xmlParseCatalogFile() is a function used to load XML Catalog files,
Daniel Veillard9f7b84b2001-08-23 15:31:19 +0000[diff] [blame]222it's similar as xmlParseFile() except it bypass all catalog lookups, it's
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]223provided because this functionality may be useful for client tools.</p><h4>threaded environments:</h4><p>Since the catalog tree is built progressively, some care has been taken to
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]224try to avoid troubles in multithreaded environments. The code is now thread
Daniel Veillard8a469172003-06-12 16:05:07 +0000[diff] [blame]225safe assuming that the libxml2 library has been compiled with threads
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]226support.</p><p></p><h3><a name="Other" id="Other">Other resources</a></h3><p>The XML Catalog specification is relatively recent so there isn't much
227literature to point at:</p><ul><li>You can find a good rant from Norm Walsh about <a href="http://www.arbortext.com/Think_Tank/XML_Resources/Issue_Three/issue_three.html">the
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]228 need for catalogs</a>, it provides a lot of context informations even if
Daniel Veillard93d3a472002-04-26 14:04:55 +0000[diff] [blame]229 I don't agree with everything presented. Norm also wrote a more recent
230 article <a href="http://wwws.sun.com/software/xml/developers/resolver/article/">XML
231 entities and URI resolvers</a> describing them.</li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]232 <li>An <a href="http://home.ccil.org/~cowan/XML/XCatalog.html">old XML
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]233 catalog proposal</a> from John Cowan</li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]234 <li>The <a href="http://www.rddl.org/">Resource Directory Description
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]235 Language</a> (RDDL) another catalog system but more oriented toward
236 providing metadata for XML namespaces.</li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]237 <li>the page from the OASIS Technical <a href="http://www.oasis-open.org/committees/entity/">Committee on Entity
Daniel Veillarde7ead2d2001-08-22 23:44:09 +0000[diff] [blame]238 Resolution</a> who maintains XML Catalog, you will find pointers to the
239 specification update, some background and pointers to others tools
240 providing XML Catalog support</li>
Daniel Veillardabfca612004-01-07 23:38:02 +0000[diff] [blame]241 <li>There is a <a href="buildDocBookCatalog">shell script</a> to generate
Daniel Veillard35e937a2002-01-19 22:21:54 +0000[diff] [blame]242 XML Catalogs for DocBook 4.1.2 . If it can write to the /etc/xml/
243 directory, it will set-up /etc/xml/catalog and /etc/xml/docbook based on
244 the resources found on the system. Otherwise it will just create
245 ~/xmlcatalog and ~/dbkxmlcatalog and doing:
Daniel Veillard8594de92003-04-25 10:08:44 +0000[diff] [blame]246 <p><code>export XML_CATALOG_FILES=$HOME/xmlcatalog</code></p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]247 <p>should allow to process DocBook documentations without requiring
Daniel Veillard63d83142002-05-20 06:51:05 +0000[diff] [blame]248 network accesses for the DTD or stylesheets</p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]249 </li>
250 <li>I have uploaded <a href="ftp://xmlsoft.org/test/dbk412catalog.tar.gz">a
Daniel Veillard35e937a2002-01-19 22:21:54 +0000[diff] [blame]251 small tarball</a> containing XML Catalogs for DocBook 4.1.2 which seems
252 to work fine for me too</li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]253 <li>The <a href="http://www.xmlsoft.org/xmlcatalog_man.html">xmlcatalog
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]254 manual page</a></li>
255</ul><p>If you have suggestions for corrections or additions, simply contact
256me:</p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>