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finished the catalog documentation Daniel
* doc/catalog.html: finished the catalog documentation Daniel
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Thu Aug 23 02:51:29 CEST 2001 Daniel Veillard <daniel@veillard.com>
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* doc/catalog.html: finished the catalog documentation
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Thu Aug 23 01:38:42 CEST 2001 Daniel Veillard <daniel@veillard.com>
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* doc/catalog.html doc/xml.html: added documentation about
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109
doc/catalog.html
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doc/catalog.html
@ -18,7 +18,7 @@ href="http://xmlsoft.org/catalog.html">http://xmlsoft.org/catalog.html</a></p>
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<p>Mailing-list archive: <a
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href="http://mail.gnome.org/archives/xml/">http://mail.gnome.org/archives/xml/</a></p>
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<p>Version: $Revision:$</p>
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<p>Version: $Revision: 1.1 $</p>
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<p>Table of Content:</p>
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<ol>
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@ -41,24 +41,23 @@ an entity (a file or a remote resource) reference another entity. The catalog
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lookup is inserted between the moment the reference is recognized by the
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software (XML parser, stylesheet processing, or even images referenced for
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inclusion in a rendering) and the time where loading that resource is
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actually started. </p>
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actually started.</p>
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<p>It is basically used for 3 things:</p>
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<ul>
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<li>mapping from "logical" names, the public identifiers and a more
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concrete name usable for download (and URI). For example it can associate
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the logical name
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<p>"-//OASIS//DTD DocBook XML V4.1.2//EN" </p>
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the logical name
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<p>"-//OASIS//DTD DocBook XML V4.1.2//EN"</p>
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<p>of the DocBook 4.1.2 XML DTD with the actual URL where it can be
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downloaded</p>
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<p>http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd </p>
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<p>http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd</p>
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</li>
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<li>remapping from a given URL to another one, like an HTTP indirection
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saying that
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<p>"http://www.oasis-open.org/committes/tr.xsl"</p>
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<p>should really be looked at</p>
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<p>"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"
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</p>
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<p>"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"</p>
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</li>
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<li>providing a local cache mechanism allowing to load the entities
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associated to public identifiers or remote resources, this is a really
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@ -77,8 +76,9 @@ actually started. </p>
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James Clark. This is relatively old and not the preferred mode of
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operation of libxml.</li>
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<li><a href="http://www.oasis-open.org/committees/entity/spec.html">XML
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Catalogs</a> is far more flexible, more recent, uses an XML syntax and
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should scale quite better. This is the default option of libxml.</li>
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Catalogs</a>
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is far more flexible, more recent, uses an XML syntax and should scale
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quite better. This is the default option of libxml.</li>
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</ul>
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<p></p>
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@ -93,7 +93,6 @@ starts with the following DOCTYPE definition:</p>
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<pre><?xml version='1.0'?>
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<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN"
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"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd">
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</pre>
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<p>When validating the document with libxml, the catalog will be
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@ -128,7 +127,7 @@ regression tests in <code>test/catalogs</code> :</p>
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written in XML, there is a specific namespace for catalog elements
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"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry in this
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catalog is a <code>public</code> mapping it allows to associate a Public
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Identifier with an URI. </p>
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Identifier with an URI.</p>
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<pre>...
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<rewriteSystem systemIdStartString="http://www.oasis-open.org/docbook/"
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rewritePrefix="file:///usr/share/xml/docbook/"/>
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@ -139,7 +138,7 @@ any URI starting with a given prefix should be looked at another URI
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constructed by replacing the prefix with an new one. In effect this acts like
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a cache system for a full area of the Web. In practice it is extremely useful
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with a file prefix if you have installed a copy of those resources on your
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local system. </p>
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local system.</p>
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<pre>...
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<delegatePublic publicIdStartString="-//OASIS//DTD XML Catalog //"
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catalog="file:///usr/share/xml/docbook.xml"/>
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@ -192,7 +191,7 @@ orchis:~/XML -> </pre>
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the base URI unavailable and the the "title.xml" entity cannot be loaded.
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Setting up the debug environment variable allows to detect that an attempt is
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made to load the <code>/etc/xml/catalog</code> but since it's not present the
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resolution fails. </p>
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resolution fails.</p>
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<p>But the most advanced way to debug XML catalog processing is to use the
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<strong>xmlcatalog</strong> command shipped with libxml2, it allows to load
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@ -276,13 +275,89 @@ orchis:~/XML -> </pre>
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exact and would have worked in a similar fashion with the Public ID
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string.</p>
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<p> This is rudimentary but should be sufficient to manage a not too complex
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catalog tree of resources. </p>
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<p>This is rudimentary but should be sufficient to manage a not too complex
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catalog tree of resources.</p>
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<h2><a name="implemento">The implementor corner quick review of the
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API:</a></h2>
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<p>@@TODO@@</p>
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<p>First an like for every other module of libxml, there is an automatically
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generated <a href="html/libxml-catalog.html">API page for catalog
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support</a>.</p>
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<p>The header for the catalog interfaces should be included as:</p>
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<pre>#include <libxml/catalog.h></pre>
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<p>The API is voluntarily kept very simple. First it is not obvious that
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applications really need access to it since it is the default behaviour of
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libxml (Note: it is possible to completely override libxml default catalog by
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using <a href="html/libxml-parser.html">xmlSetExternalEntityLoader</a> to
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plug an application specific resolver).</p>
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<p>Basically libxml support 2 catalog lists:</p>
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<ul>
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<li>the default one, global shared by all the application</li>
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<li>a per-document catalog, this one is built if the document uses the
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<code>oasis-xml-catalog</code> PIs to specify its own catalog list, it is
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associated to the parser context and destroyed when the parsing context
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is destroyed.</li>
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</ul>
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<p>the document one will be used first if it exists.</p>
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<h3>Initialization routines:</h3>
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<p>xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs() should be
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used at startup to initialize the catalog, if the catalog should be
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initialized with specific values xmlLoadCatalog() or xmlLoadCatalogs()
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should be called before xmlInitializeCatalog() which would otherwise do a
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default initialization first.</p>
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<p>The xmlCatalogAddLocal() call is used by the parser to grow the document
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own catalog list if needed.</p>
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<h3>Preferences setup:</h3>
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<p>The XML Catalog spec requires the possibility to select default
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preferences between public and system delegation,
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xmlCatalogSetDefaultPrefer() allows this, xmlCatalogSetDefaults() and
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xmlCatalogGetDefaults() allow to control if XML Catalogs resolution should
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be forbidden, allowed for global catalog, for document catalog or both, the
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default is to allow both.</p>
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<p>And of course xmlCatalogSetDebug() allows to generate debug messages
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(through the xmlGenericError() mechanism).</p>
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<h3>Querying routines:</h3>
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<p>xmlCatalogResolve(), xmlCatalogResolveSystem(), xmlCatalogResolvePublic()
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and xmlCatalogResolveURI() are relatively explicit if you read the XML
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Catalog specification they correspond to section 7 algorithms, they should
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also work if you have loaded an SGML catalog with a simplified semantic.</p>
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<p>xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the same but
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operate on the document catalog list</p>
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<h3>Cleanup and Miscellaneous:</h3>
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<p>xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal() is
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the per-document equivalent.</p>
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<p>xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically modify the
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first catalog in the global list, and xmlCatalogDump() allows to dump a
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catalog state, those routines are primarily designed for xmlcatalog, I'm not
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sure that exposing more complex interfaces (like navigation ones) would be
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really useful.</p>
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<h3>threaded environments:</h3>
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<p>Since the catalog tree is built progressively, some care has been taken to
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try to avoid troubles in multithreaded environments but without a
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test-and-set routine accessible from C this can't be fully garanteed, so the
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best is to use xmlGetExternalEntityLoader and set the entity loader routines
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to one of your code doing the synchronization.</p>
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<p></p>
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<h2><a name="Other">Other resources</a></h2>
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@ -310,6 +385,6 @@ me:</p>
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<p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p>
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<p>$Id:$</p>
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<p>$Id: catalog.html,v 1.1 2001/08/22 23:44:08 veillard Exp $</p>
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</body>
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</html>
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