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@@ -14,78 +14,77 @@ A:link, A:visited, A:active { text-decoration: underline }
<li><a href="#reference">How to tune catalog usage</a></li>
<li><a href="#validate">How to debug catalog processing</a></li>
<li><a href="#Declaring">How to create and maintain catalogs</a></li>
- <li><a href="#implemento">The implementor corner quick review
- oftheAPI</a></li>
+ <li><a href="#implemento">The implementor corner quick review of the
+ API</a></li>
<li><a href="#Other">Other resources</a></li>
-</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(afile or a remote resource) references another entity. The catalog
-lookupisinserted between the moment the reference is recognized by the
-software(XMLparser, stylesheet processing, or even images referenced for
-inclusionin arendering) and the time where loading that resource is
-actuallystarted.</p><p>It is basically used for 3 things:</p><ul><li>mapping from "logical" names, the public identifiers and a
- moreconcretename usable for download (and URI). For example it can
- associatethelogical name
+</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
+(a file or a remote resource) references another entity. The catalog lookup
+is inserted between the moment the reference is recognized by the software
+(XML parser, stylesheet processing, or even images referenced for inclusion
+in a rendering) and the time where loading that resource is actually
+started.</p><p>It is basically used for 3 things:</p><ul><li>mapping from "logical" names, the public identifiers and a more
+ concrete name usable for download (and URI). For example it can associate
+ the logical name
<p>"-//OASIS//DTD DocBook XML V4.1.2//EN"</p>
- <p>of the DocBook 4.1.2 XML DTD with the actual URL where it
- canbedownloaded</p>
+ <p>of the DocBook 4.1.2 XML DTD with the actual URL where it can be
+ downloaded</p>
<p>http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd</p>
</li>
- <li>remapping from a given URL to another one, like an
- HTTPindirectionsaying that
+ <li>remapping from a given URL to another one, like an HTTP indirection
+ saying that
<p>"http://www.oasis-open.org/committes/tr.xsl"</p>
<p>should really be looked at</p>
<p>"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"</p>
</li>
- <li>providing a local cache mechanism allowing to load
- theentitiesassociated to public identifiers or remote resources, this is
- areallyimportant feature for any significant deployment of XML or
- SGMLsince itallows to avoid the aleas and delays associated to
- fetchingremoteresources.</li>
-</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
- OpenTechnicalResolution TR9401:1997, but is better understood by reading
- <a href="http://www.jclark.com/sp/catalog.htm">the SP
- Catalogpage</a>fromJames Clark. This is relatively old and not the
- preferredmode ofoperation of libxml.</li>
- <li><a href="http://www.oasis-open.org/committees/entity/spec.html">XMLCatalogs</a>isfar
- more flexible, more recent, uses an XML syntax andshould scale
- quitebetter. This is the default option of libxml.</li>
-</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
-ofacatalog in /etc/xml/catalog, and assuming it has been
-correctlypopulated,the processing is completely transparent to the document
-user. Totake aconcrete example, suppose you are authoring a DocBook document,
-thisonestarts with the following DOCTYPE definition:</p><pre>&lt;?xml version='1.0'?&gt;
+ <li>providing a local cache mechanism allowing to load the entities
+ associated to public identifiers or remote resources, this is a really
+ important feature for any significant deployment of XML or SGML since it
+ allows to avoid the aleas and delays associated to fetching remote
+ resources.</li>
+</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
+ Resolution TR9401:1997, but is better understood by reading <a href="http://www.jclark.com/sp/catalog.htm">the SP Catalog page</a> from
+ James Clark. This is relatively old and not the preferred mode of
+ operation of libxml.</li>
+ <li><a href="http://www.oasis-open.org/committees/entity/spec.html">XML
+ Catalogs</a> is far more flexible, more recent, uses an XML syntax and
+ should scale quite better. This is the default option of libxml.</li>
+</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
+catalog in /etc/xml/catalog, and assuming it has been correctly populated,
+the processing is completely transparent to the document user. To take a
+concrete example, suppose you are authoring a DocBook document, this one
+starts with the following DOCTYPE definition:</p><pre>&lt;?xml version='1.0'?&gt;
&lt;!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN"
- "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd"&gt;</pre><p>When validating the document with libxml, the catalog will
-beautomaticallyconsulted to lookup the public identifier "-//Norman
-Walsh//DTDDocBk XMLV3.1.4//EN" and the
-systemidentifier"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd", and if
-theseentities havebeen installed on your system and the catalogs actually
-point tothem, libxmlwill fetch them from the local disk.</p><p style="font-size: 10pt"><strong>Note</strong>: Really don't usethisDOCTYPE
-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
-loadanentity, this includes DTD, external parsed entities, stylesheets, etc
-...Ifyour system is correctly configured all the authoring phase
-andprocessingshould use only local files, even if your document stays
-portablebecause ituses the canonical public and system ID, referencing the
-remotedocument.</p><h3><a name="Some" id="Some">Some examples:</a></h3><p>Here is a couple of fragments from XML Catalogs used in
-libxml2earlyregression tests in <code>test/catalogs</code>:</p><pre>&lt;?xml version="1.0"?&gt;
+ "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd"&gt;</pre><p>When validating the document with libxml, the catalog will be
+automatically consulted to lookup the public identifier "-//Norman Walsh//DTD
+DocBk XML V3.1.4//EN" and the system identifier
+"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd", and if these entities have
+been installed on your system and the catalogs actually point to them, libxml
+will fetch them from the local disk.</p><p style="font-size: 10pt"><strong>Note</strong>: Really don't use this
+DOCTYPE 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
+entity, this includes DTD, external parsed entities, stylesheets, etc ... If
+your system is correctly configured all the authoring phase and processing
+should use only local files, even if your document stays portable because it
+uses 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
+regression tests in <code>test/catalogs</code> :</p><pre>&lt;?xml version="1.0"?&gt;
&lt;!DOCTYPE catalog PUBLIC
"-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
"http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"&gt;
&lt;catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"&gt;
&lt;public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/&gt;
-...</pre><p>This is the beginning of a catalog for DocBook 4.1.2, XML
-Catalogsarewritten in XML, there is a specific namespace for
-catalogelements"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry
-inthiscatalog is a <code>public</code>mapping it allows to associate
-aPublicIdentifier with an URI.</p><pre>...
+...</pre><p>This is the beginning of a catalog for DocBook 4.1.2, XML Catalogs are
+written in XML, there is a specific namespace for catalog elements
+"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry in this
+catalog is a <code>public</code> mapping it allows to associate a Public
+Identifier with an URI.</p><pre>...
&lt;rewriteSystem systemIdStartString="http://www.oasis-open.org/docbook/"
rewritePrefix="file:///usr/share/xml/docbook/"/&gt;
-...</pre><p>A <code>rewriteSystem</code>is a very powerful instruction, it saysthatany
-URI starting with a given prefix should be looked at anotherURIconstructed by
-replacing the prefix with an new one. In effect this actslikea cache system
-for a full area of the Web. In practice it is extremelyusefulwith a file
-prefix if you have installed a copy of those resources onyourlocal system.</p><pre>...
+...</pre><p>A <code>rewriteSystem</code> is a very powerful instruction, it says that
+any URI starting with a given prefix should be looked at another URI
+constructed by replacing the prefix with an new one. In effect this acts like
+a cache system for a full area of the Web. In practice it is extremely useful
+with a file prefix if you have installed a copy of those resources on your
+local system.</p><pre>...
&lt;delegatePublic publicIdStartString="-//OASIS//DTD XML Catalog //"
catalog="file:///usr/share/xml/docbook.xml"/&gt;
&lt;delegatePublic publicIdStartString="-//OASIS//ENTITIES DocBook XML"
@@ -96,21 +95,21 @@ prefix if you have installed a copy of those resources onyourlocal system.</p><p
catalog="file:///usr/share/xml/docbook.xml"/&gt;
&lt;delegateURI uriStartString="http://www.oasis-open.org/docbook/"
catalog="file:///usr/share/xml/docbook.xml"/&gt;
-...</pre><p>Delegation is the core features which allows to build a tree
-ofcatalogs,easier to maintain than a single catalog, based on
-PublicIdentifier, SystemIdentifier or URI prefixes it instructs the
-catalogsoftware to look upentries in another resource. This feature allow to
-buildhierarchies ofcatalogs, the set of entries presented should be
-sufficient toredirect theresolution of all DocBook references to the specific
-catalogin<code>/usr/share/xml/docbook.xml</code>this one in turn could
-delegateallreferences for DocBook 4.2.1 to a specific catalog installed at
-the sametimeas 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
-queriestoits own set of catalogs, this can be done by
-settingthe<code>XML_CATALOG_FILES</code>environment variable to a list of
-catalogs,anempty one should deactivate loading the
-default<code>/etc/xml/catalog</code>default 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
-willmakelibxml2 output debugging informations for each catalog
-operations,forexample:</p><pre>orchis:~/XML -&gt; xmllint --memory --noout test/ent2
+...</pre><p>Delegation is the core features which allows to build a tree of catalogs,
+easier to maintain than a single catalog, based on Public Identifier, System
+Identifier or URI prefixes it instructs the catalog software to look up
+entries in another resource. This feature allow to build hierarchies of
+catalogs, the set of entries presented should be sufficient to redirect the
+resolution of all DocBook references to the specific catalog in
+<code>/usr/share/xml/docbook.xml</code> this one in turn could delegate all
+references for DocBook 4.2.1 to a specific catalog installed at the same time
+as 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
+to its own set of catalogs, this can be done by setting the
+<code>XML_CATALOG_FILES</code> environment variable to a list of catalogs, an
+empty one should deactivate loading the default <code>/etc/xml/catalog</code>
+default 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
+make libxml2 output debugging informations for each catalog operations, for
+example:</p><pre>orchis:~/XML -&gt; xmllint --memory --noout test/ent2
warning: failed to load external entity "title.xml"
orchis:~/XML -&gt; export XML_DEBUG_CATALOG=
orchis:~/XML -&gt; xmllint --memory --noout test/ent2
@@ -118,26 +117,26 @@ Failed to parse catalog /etc/xml/catalog
Failed to parse catalog /etc/xml/catalog
warning: failed to load external entity "title.xml"
Catalogs cleanup
-orchis:~/XML -&gt; </pre><p>The test/ent2 references an entity, running the parser from memorymakesthe
-base URI unavailable and the the "title.xml" entity cannot beloaded.Setting
-up the debug environment variable allows to detect that anattempt ismade to
-load the <code>/etc/xml/catalog</code>but since it's notpresent theresolution
-fails.</p><p>But the most advanced way to debug XML catalog processing is to
-usethe<strong>xmlcatalog</strong>command shipped with libxml2, it allows
-toloadcatalogs and make resolution queries to see what is going on. This
-isalsoused for the regression tests:</p><pre>orchis:~/XML -&gt; ./xmlcatalog test/catalogs/docbook.xml \
+orchis:~/XML -&gt; </pre><p>The test/ent2 references an entity, running the parser from memory makes
+the base URI unavailable and the the "title.xml" entity cannot be loaded.
+Setting up the debug environment variable allows to detect that an attempt is
+made to load the <code>/etc/xml/catalog</code> but since it's not present the
+resolution fails.</p><p>But the most advanced way to debug XML catalog processing is to use the
+<strong>xmlcatalog</strong> command shipped with libxml2, it allows to load
+catalogs and make resolution queries to see what is going on. This is also
+used for the regression tests:</p><pre>orchis:~/XML -&gt; ./xmlcatalog test/catalogs/docbook.xml \
"-//OASIS//DTD DocBook XML V4.1.2//EN"
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
-orchis:~/XML -&gt; </pre><p>For debugging what is going on, adding one -v flags increase
-theverbositylevel to indicate the processing done (adding a second flag
-alsoindicatewhat elements are recognized at parsing):</p><pre>orchis:~/XML -&gt; ./xmlcatalog -v test/catalogs/docbook.xml \
+orchis:~/XML -&gt; </pre><p>For debugging what is going on, adding one -v flags increase the verbosity
+level to indicate the processing done (adding a second flag also indicate
+what elements are recognized at parsing):</p><pre>orchis:~/XML -&gt; ./xmlcatalog -v test/catalogs/docbook.xml \
"-//OASIS//DTD DocBook XML V4.1.2//EN"
Parsing catalog test/catalogs/docbook.xml's content
Found public match -//OASIS//DTD DocBook XML V4.1.2//EN
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
Catalogs cleanup
-orchis:~/XML -&gt; </pre><p>A shell interface is also available to debug and process
-multiplequeries(and for regression tests):</p><pre>orchis:~/XML -&gt; ./xmlcatalog -shell test/catalogs/docbook.xml \
+orchis:~/XML -&gt; </pre><p>A shell interface is also available to debug and process multiple queries
+(and for regression tests):</p><pre>orchis:~/XML -&gt; ./xmlcatalog -shell test/catalogs/docbook.xml \
"-//OASIS//DTD DocBook XML V4.1.2//EN"
&gt; help
Commands available:
@@ -153,18 +152,18 @@ exit: quit the shell
&gt; public "-//OASIS//DTD DocBook XML V4.1.2//EN"
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
&gt; quit
-orchis:~/XML -&gt; </pre><p>This should be sufficient for most debugging purpose, this wasactuallyused
-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 toolstomanage
-them or use <strong>xmlcatalog</strong>for this. The basic stepisto create a
-catalog the -create option provide this facility:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --create tst.xml
+orchis:~/XML -&gt; </pre><p>This should be sufficient for most debugging purpose, this was actually
+used 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
+manage them or use <strong>xmlcatalog</strong> for this. The basic step is
+to create a catalog the -create option provide this facility:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --create tst.xml
&lt;?xml version="1.0"?&gt;
&lt;!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
"http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"&gt;
&lt;catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/&gt;
-orchis:~/XML -&gt; </pre><p>By default xmlcatalog does not overwrite the original catalog and
-savetheresult on the standard output, this can be overridden using
-the-nooutoption. The <code>-add</code>command allows to add entries
-inthecatalog:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --noout --create --add "public" \
+orchis:~/XML -&gt; </pre><p>By default xmlcatalog does not overwrite the original catalog and save the
+result on the standard output, this can be overridden using the -noout
+option. The <code>-add</code> command allows to add entries in the
+catalog:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --noout --create --add "public" \
"-//OASIS//DTD DocBook XML V4.1.2//EN" \
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd tst.xml
orchis:~/XML -&gt; cat tst.xml
@@ -175,80 +174,83 @@ orchis:~/XML -&gt; cat tst.xml
&lt;public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/&gt;
&lt;/catalog&gt;
-orchis:~/XML -&gt; </pre><p>The <code>-add</code>option will always take 3 parameters even if
-someofthe XML Catalog constructs (like nextCatalog) will have only
-asingleargument, just pass a third empty string, it will be ignored.</p><p>Similarly the <code>-del</code>option remove matching entries
-fromthecatalog:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --del \
+orchis:~/XML -&gt; </pre><p>The <code>-add</code> option will always take 3 parameters even if some of
+the XML Catalog constructs (like nextCatalog) will have only a single
+argument, just pass a third empty string, it will be ignored.</p><p>Similarly the <code>-del</code> option remove matching entries from the
+catalog:</p><pre>orchis:~/XML -&gt; ./xmlcatalog --del \
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" tst.xml
&lt;?xml version="1.0"?&gt;
&lt;!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
"http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"&gt;
&lt;catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/&gt;
-orchis:~/XML -&gt; </pre><p>The catalog is now empty. Note that the matching
-of<code>-del</code>isexact and would have worked in a similar fashion with
-thePublic IDstring.</p><p>This is rudimentary but should be sufficient to manage a not
-toocomplexcatalog tree of resources.</p><h3><a name="implemento" id="implemento">The implementor corner quick review
-oftheAPI:</a></h3><p>First, and like for every other module of libxml, there is
-anautomaticallygenerated <a href="html/libxml-catalog.html">API page
-forcatalogsupport</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
-obviousthatapplications really need access to it since it is the default
-behaviouroflibxml2 (Note: it is possible to completely override libxml2
-defaultcatalogby using <a href="html/libxml-parser.html">xmlSetExternalEntityLoader</a>toplug
-anapplication specific resolver).</p><p>Basically libxml2 support 2 catalog lists:</p><ul><li>the default one, global shared by all the application</li>
- <li>a per-document catalog, this one is built if the document
- usesthe<code>oasis-xml-catalog</code>PIs to specify its own catalog list,
- itisassociated to the parser context and destroyed when the
- parsingcontextis destroyed.</li>
-</ul><p>the document one will be used first if it exists.</p><h4>Initialization routines:</h4><p>xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs()
-shouldbeused at startup to initialize the catalog, if the catalog
-shouldbeinitialized with specific values xmlLoadCatalog()
-orxmlLoadCatalogs()should be called before xmlInitializeCatalog() which
-wouldotherwise do adefault initialization first.</p><p>The xmlCatalogAddLocal() call is used by the parser to grow thedocumentown
-catalog list if needed.</p><h4>Preferences setup:</h4><p>The XML Catalog spec requires the possibility to select
-defaultpreferencesbetween public and system
-delegation,xmlCatalogSetDefaultPrefer() allowsthis, xmlCatalogSetDefaults()
-andxmlCatalogGetDefaults() allow to control ifXML Catalogs resolution
-shouldbe forbidden, allowed for global catalog, fordocument catalog or both,
-thedefault is to allow both.</p><p>And of course xmlCatalogSetDebug() allows to generate
-debugmessages(through the xmlGenericError() mechanism).</p><h4>Querying routines:</h4><p>xmlCatalogResolve(),
-xmlCatalogResolveSystem(),xmlCatalogResolvePublic()and xmlCatalogResolveURI()
-are relatively explicitif you read the XMLCatalog specification they
-correspond to section 7algorithms, they shouldalso work if you have loaded an
-SGML catalog with asimplified semantic.</p><p>xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the
-samebutoperate on the document catalog list</p><h4>Cleanup and Miscellaneous:</h4><p>xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal()isthe
-per-document equivalent.</p><p>xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically
-modifythefirst catalog in the global list, and xmlCatalogDump() allows to
-dumpacatalog state, those routines are primarily designed for xmlcatalog,
-I'mnotsure that exposing more complex interfaces (like navigation ones)
-wouldbereally useful.</p><p>The xmlParseCatalogFile() is a function used to load XML Catalogfiles,it's
-similar as xmlParseFile() except it bypass all catalog lookups,it'sprovided
-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
-takentotry to avoid troubles in multithreaded environments. The code is
-nowthreadsafe assuming that the libxml2 library has been compiled
-withthreadssupport.</p><p></p><h3><a name="Other" id="Other">Other resources</a></h3><p>The XML Catalog specification is relatively recent so there
-isn'tmuchliterature 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">theneedfor
- catalogs</a>, it provides a lot of context informations even ifIdon't
- agree with everything presented. Norm also wrote a morerecentarticle <a href="http://wwws.sun.com/software/xml/developers/resolver/article/">XMLentitiesand
- URI resolvers</a>describing them.</li>
- <li>An <a href="http://home.ccil.org/~cowan/XML/XCatalog.html">oldXMLcatalog
- proposal</a>from John Cowan</li>
- <li>The <a href="http://www.rddl.org/">Resource
- DirectoryDescriptionLanguage</a>(RDDL) another catalog system but more
- orientedtowardproviding metadata for XML namespaces.</li>
- <li>the page from the OASIS Technical <a href="http://www.oasis-open.org/committees/entity/">Committee
- onEntityResolution</a>who maintains XML Catalog, you will find pointers
- tothespecification update, some background and pointers to
- otherstoolsproviding XML Catalog support</li>
- <li>There is a <a href="buildDocBookCatalog">shell script</a>to
- generateXMLCatalogs for DocBook 4.1.2 . If it can write to the
- /etc/xml/directory,it will set-up /etc/xml/catalog and /etc/xml/docbook
- based ontheresources found on the system. Otherwise it will just
- create~/xmlcatalogand ~/dbkxmlcatalog and doing:
+orchis:~/XML -&gt; </pre><p>The catalog is now empty. Note that the matching of <code>-del</code> is
+exact and would have worked in a similar fashion with the Public ID
+string.</p><p>This is rudimentary but should be sufficient to manage a not too complex
+catalog tree of resources.</p><h3><a name="implemento" id="implemento">The implementor corner quick review of the
+API:</a></h3><p>First, and like for every other module of libxml, there is an
+automatically generated <a href="html/libxml-catalog.html">API page for
+catalog 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
+applications really need access to it since it is the default behaviour of
+libxml2 (Note: it is possible to completely override libxml2 default catalog
+by using <a href="html/libxml-parser.html">xmlSetExternalEntityLoader</a> to
+plug 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>
+ <li>a per-document catalog, this one is built if the document uses the
+ <code>oasis-xml-catalog</code> PIs to specify its own catalog list, it is
+ associated to the parser context and destroyed when the parsing context
+ is destroyed.</li>
+</ul><p>the document one will be used first if it exists.</p><h4>Initialization routines:</h4><p>xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs() should be
+used at startup to initialize the catalog, if the catalog should be
+initialized with specific values xmlLoadCatalog() or xmlLoadCatalogs()
+should be called before xmlInitializeCatalog() which would otherwise do a
+default initialization first.</p><p>The xmlCatalogAddLocal() call is used by the parser to grow the document
+own catalog list if needed.</p><h4>Preferences setup:</h4><p>The XML Catalog spec requires the possibility to select default
+preferences between public and system delegation,
+xmlCatalogSetDefaultPrefer() allows this, xmlCatalogSetDefaults() and
+xmlCatalogGetDefaults() allow to control if XML Catalogs resolution should
+be forbidden, allowed for global catalog, for document catalog or both, the
+default is to allow both.</p><p>And of course xmlCatalogSetDebug() allows to generate debug messages
+(through the xmlGenericError() mechanism).</p><h4>Querying routines:</h4><p>xmlCatalogResolve(), xmlCatalogResolveSystem(), xmlCatalogResolvePublic()
+and xmlCatalogResolveURI() are relatively explicit if you read the XML
+Catalog specification they correspond to section 7 algorithms, they should
+also work if you have loaded an SGML catalog with a simplified semantic.</p><p>xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the same but
+operate on the document catalog list</p><h4>Cleanup and Miscellaneous:</h4><p>xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal() is
+the per-document equivalent.</p><p>xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically modify the
+first catalog in the global list, and xmlCatalogDump() allows to dump a
+catalog state, those routines are primarily designed for xmlcatalog, I'm not
+sure that exposing more complex interfaces (like navigation ones) would be
+really useful.</p><p>The xmlParseCatalogFile() is a function used to load XML Catalog files,
+it's similar as xmlParseFile() except it bypass all catalog lookups, it's
+provided 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
+try to avoid troubles in multithreaded environments. The code is now thread
+safe assuming that the libxml2 library has been compiled with threads
+support.</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
+literature 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
+ need for catalogs</a>, it provides a lot of context informations even if
+ I don't agree with everything presented. Norm also wrote a more recent
+ article <a href="http://wwws.sun.com/software/xml/developers/resolver/article/">XML
+ entities and URI resolvers</a> describing them.</li>
+ <li>An <a href="http://home.ccil.org/~cowan/XML/XCatalog.html">old XML
+ catalog proposal</a> from John Cowan</li>
+ <li>The <a href="http://www.rddl.org/">Resource Directory Description
+ Language</a> (RDDL) another catalog system but more oriented toward
+ providing metadata for XML namespaces.</li>
+ <li>the page from the OASIS Technical <a href="http://www.oasis-open.org/committees/entity/">Committee on Entity
+ Resolution</a> who maintains XML Catalog, you will find pointers to the
+ specification update, some background and pointers to others tools
+ providing XML Catalog support</li>
+ <li>There is a <a href="buildDocBookCatalog">shell script</a> to generate
+ XML Catalogs for DocBook 4.1.2 . If it can write to the /etc/xml/
+ directory, it will set-up /etc/xml/catalog and /etc/xml/docbook based on
+ the resources found on the system. Otherwise it will just create
+ ~/xmlcatalog and ~/dbkxmlcatalog and doing:
<p><code>export XML_CATALOG_FILES=$HOME/xmlcatalog</code></p>
- <p>should allow to process DocBook documentations withoutrequiringnetwork
- accesses for the DTD or stylesheets</p>
+ <p>should allow to process DocBook documentations without requiring
+ network accesses for the DTD or stylesheets</p>
</li>
- <li>I have uploaded <a href="ftp://xmlsoft.org/libxml2/test/dbk412catalog.tar.gz">asmalltarball</a>containing
- XML Catalogs for DocBook 4.1.2 which seemsto workfine for me too</li>
- <li>The <a href="http://www.xmlsoft.org/xmlcatalog_man.html">xmlcatalogmanualpage</a></li>
-</ul><p>If you have suggestions for corrections or additions, simply contactme:</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>
+ <li>I have uploaded <a href="ftp://xmlsoft.org/libxml2/test/dbk412catalog.tar.gz">a
+ small tarball</a> containing XML Catalogs for DocBook 4.1.2 which seems
+ to work fine for me too</li>
+ <li>The <a href="http://www.xmlsoft.org/xmlcatalog_man.html">xmlcatalog
+ manual page</a></li>
+</ul><p>If you have suggestions for corrections or additions, simply contact
+me:</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>