Google Git
Sign in
fuchsia / third_party / libxml2 / 3bbbe6fa2a16ce1e1c1ff08725cf09857d7c0428 / . / doc / xml.html
blob: 90e125e823e0eb870f79c99c7c32cf31905eff4f [file] [log] [blame]
<html>
<head>
<title>The XML C library for Gnome</title>
<meta name="GENERATOR" content="amaya V4.1">
<meta http-equiv="Content-Type" content="text/html">
</head>
<body bgcolor="#ffffff">
<p><a href="http://www.gnome.org/"><img src="smallfootonly.gif"
alt="Gnome Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png"
alt="W3C Logo"></a></p>
<h1 align="center">The XML C library for Gnome</h1>
<h2 style="text-align: center">libxml, a.k.a. gnome-xml</h2>
<p></p>
<ul>
<li><a href="#Introducti">Introduction</a></li>
<li><a href="#Documentat">Documentation</a></li>
<li><a href="#Reporting">Reporting bugs and getting help</a></li>
<li><a href="#help">how to help</a></li>
<li><a href="#Downloads">Downloads</a></li>
<li><a href="#News">News</a></li>
<li><a href="#XML">XML</a></li>
<li><a href="#XSLT">XSLT</a></li>
<li><a href="#tree">The tree output</a></li>
<li><a href="#interface">The SAX interface</a></li>
<li><a href="#library">The XML library interfaces</a>
<ul>
<li><a href="#Invoking">Invoking the parser: the pull way</a></li>
<li><a href="#Invoking">Invoking the parser: the push way</a></li>
<li><a href="#Invoking2">Invoking the parser: the SAX interface</a></li>
<li><a href="#Building">Building a tree from scratch</a></li>
<li><a href="#Traversing">Traversing the tree</a></li>
<li><a href="#Modifying">Modifying the tree</a></li>
<li><a href="#Saving">Saving the tree</a></li>
<li><a href="#Compressio">Compression</a></li>
</ul>
</li>
<li><a href="#Entities">Entities or no entities</a></li>
<li><a href="#Namespaces">Namespaces</a></li>
<li><a href="#Validation">Validation</a></li>
<li><a href="#Principles">DOM principles</a></li>
<li><a href="#real">A real example</a></li>
<li><a href="#Contributi">Contributions</a></li>
</ul>
<p>Separate documents:</p>
<ul>
<li><a href="upgrade.html">upgrade instructions for migrating to
libxml2</a></li>
<li><a href="encoding.html">libxml Internationalization support</a></li>
<li><a href="xmlio.html">libxml Input/Output interfaces</a></li>
<li><a href="xmlmem.html">libxml Memory interfaces</a></li>
<li><a href="xmldtd.html">a short introduction about DTDs and
libxml</a></li>
<li><a href="http://xmlsoft.org/XSLT/">the libxslt page</a></li>
</ul>
<h2><a name="Introducti">Introduction</a></h2>
<p>This document describes libxml, the <a
href="http://www.w3.org/XML/">XML</a> C library developped for the <a
href="http://www.gnome.org/">Gnome</a> project. <a
href="http://www.w3.org/XML/">XML is a standard</a> for building tag-based
structured documents/data.</p>
<p>Here are some key points about libxml:</p>
<ul>
<li>Libxml exports Push and Pull type parser interfaces for both XML and
HTML.</li>
<li>Libxml can do DTD validation at parse time, using a parsed document
instance, or with an arbitrary DTD.</li>
<li>Libxml now includes nearly complete <a
href="http://www.w3.org/TR/xpath">XPath</a> and <a
href="http://www.w3.org/TR/xptr">XPointer</a> implementations.</li>
<li>It is written in plain C, making as few assumptions as possible, and
sticking closely to ANSI C/POSIX for easy embedding. Works on
Linux/Unix/Windows, ported to a number of other platforms.</li>
<li>Basic support for HTTP and FTP client allowing aplications to fetch
remote resources</li>
<li>The design is modular, most of the extensions can be compiled out.</li>
<li>The internal document repesentation is as close as possible to the <a
href="http://www.w3.org/DOM/">DOM</a> interfaces.</li>
<li>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX
like interface</a>; the interface is designed to be compatible with <a
href="http://www.jclark.com/xml/expat.html">Expat</a>.</li>
<li>This library is released both under the <a
href="http://www.w3.org/Consortium/Legal/copyright-software-19980720.html">W3C
IPR</a> and the <a href="http://www.gnu.org/copyleft/lesser.html">GNU
LGPL</a>. Use either at your convenience, basically this should make
everybody happy, if not, drop me a mail.</li>
</ul>
<p>Warning: unless you are forced to because your application links with a
Gnome library requiring it, <strong><span
style="background-color: #FF0000">Do Not Use libxml1</span></strong>, use
libxml2</p>
<h2><a name="Documentat">Documentation</a></h2>
<p>There are some on-line resources about using libxml:</p>
<ol>
<li>Check the <a href="FAQ.html">FAQ</a></li>
<li>Check the <a href="http://xmlsoft.org/html/libxml-lib.html">extensive
documentation</a> automatically extracted from code comments (using <a
href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&amp;dir=gtk-doc">gtk
doc</a>).</li>
<li>Look at the documentation about <a href="encoding.html">libxml
internationalization support</a></li>
<li>This page provides a global overview and <a href="#real">some
examples</a> on how to use libxml.</li>
<li><a href="mailto:james@daa.com.au">James Henstridge</a> wrote <a
href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">some nice
documentation</a> explaining how to use the libxml SAX interface.</li>
<li>George Lebl wrote <a
href="http://www-4.ibm.com/software/developer/library/gnome3/">an article
for IBM developerWorks</a> about using libxml.</li>
<li>It is also a good idea to check to <a href="mailto:raph@levien.com">Raph
Levien</a>'s <a href="http://levien.com/gnome/">web site</a> since he is
building the <a href="http://levien.com/gnome/gdome.html">DOM interface
gdome</a> on top of libxml result tree and an implementation of <a
href="http://www.w3.org/Graphics/SVG/">SVG</a> called <a
href="http://www.levien.com/svg/">gill</a>. Check his <a
href="http://www.levien.com/gnome/domination.html">DOMination
paper</a>.</li>
<li>Check <a href="http://cvs.gnome.org/lxr/source/gnome-xml/TODO">the TODO
file</a></li>
<li>Read the <a href="upgrade.html">1.x to 2.x upgrade path</a>. If you are
starting a new project using libxml you should really use the 2.x
version.</li>
<li>And don't forget to look at the <a href="/messages/">mailing-list
archive</a>.</li>
</ol>
<h2><a name="Reporting">Reporting bugs and getting help</a></h2>
<p>Well, bugs or missing features are always possible, and I will make a point
of fixing them in a timely fashion. The best way to report a bug is to use the
<a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Gnome bug
tracking database</a> (make sure to use the "libxml" module name). I look at
reports there regularly and it's good to have a reminder when a bug is still
open. Check the <a
href="http://bugzilla.gnome.org/bugwritinghelp.html">instructions on reporting
bugs</a> and be sure to specify that the bug is for the package libxml.</p>
<p>There is also a mailing-list <a
href="mailto:xml@gnome.org">xml@gnome.org</a> for libxml, with an <a
href="http://mail.gnome.org/archives/xml/">on-line archive</a> (<a
href="http://xmlsoft.org/messages">old</a>). To subscribe to this list, please
visit the <a href="http://mail.gnome.org/mailman/listinfo/xml">associated
Web</a> page and follow the instructions.</p>
<p>Alternatively, you can just send the bug to the <a
href="mailto:xml@gnome.org">xml@gnome.org</a> list; if it's really libxml
related I will approve it..</p>
<p>Of course, bugs reported with a suggested patch for fixing them will
probably be processed faster.</p>
<p>If you're looking for help, a quick look at <a
href="http://xmlsoft.org/messages/#407">the list archive</a> may actually
provide the answer, I usually send source samples when answering libxml usage
questions. The <a href="http://xmlsoft.org/html/book1.html">auto-generated
documentantion</a> is not as polished as I would like (i need to learn more
about Docbook), but it's a good starting point.</p>
<h2><a name="help">How to help</a></h2>
<p>You can help the project in various ways, the best thing to do first is to
subscribe to the mailing-list as explained before, check the <a
href="http://xmlsoft.org/messages/">archives </a>and the <a
href="http://bugs.gnome.org/db/pa/lgnome-xml.html">Gnome bug
database:</a>:</p>
<ol>
<li>provide patches when you find problems</li>
<li>provide the diffs when you port libxml to a new platform. They may not
be integrated in all cases but help pinpointing portability problems
and</li>
<li>provide documentation fixes (either as patches to the code comments or
as HTML diffs).</li>
<li>provide new documentations pieces (translations, examples, etc ...)</li>
<li>Check the TODO file and try to close one of the items</li>
<li>take one of the points raised in the archive or the bug database and
provide a fix. <a href="mailto:Daniel.Veillard@imag.fr">Get in touch with
me </a>before to avoid synchronization problems and check that the
suggested fix will fit in nicely :-)</li>
</ol>
<h2><a name="Downloads">Downloads</a></h2>
<p>The latest versions of libxml can be found on <a
href="ftp://xmlsoft.org/">xmlsoft.org</a> or on the <a
href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either
as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source
archive</a> or <a
href="ftp://ftp.gnome.org/pub/GNOME/stable/redhat/i386/libxml/">RPM
packages</a>. (NOTE that you need both the <a
href="http://rpmfind.net/linux/RPM/libxml2.html">libxml(2)</a> and <a
href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml(2)-devel</a>
packages installed to compile applications using libxml.)</p>
<p><a name="Snapshot">Snapshot:</a></p>
<ul>
<li>Code from the W3C cvs base libxml <a
href="ftp://xmlsoft.org/cvs-snapshot.tar.gz">cvs-snapshot.tar.gz</a></li>
<li>Docs, content of the web site, the list archive included <a
href="ftp://xmlsoft.org/libxml-docs.tar.gz">libxml-docs.tar.gz</a></li>
</ul>
<p><a name="Contribs">Contribs:</a></p>
<p>I do accept external contributions, especially if compiling on another
platform, get in touch with me to upload the package. I will keep them in the
<a href="ftp://xmlsoft.org/contribs/">contrib directory</a></p>
<p>Libxml is also available from CVS:</p>
<ul>
<li><p>The <a
href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&amp;dir=gnome-xml">Gnome
CVS base</a>. Check the <a
href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> page;
the CVS module is <b>gnome-xml</b>.</p>
</li>
<li>The <strong>libxslt</strong> module is also present there</li>
</ul>
<h2><a name="News">News</a></h2>
<h3>CVS only : check the <a
href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file
for a really accurate description</h3>
<p>Items floating around but not actively worked on, get in touch with me if
you want to test those</p>
<ul>
<li>Implementing <a href="http://xmlsoft.org/XSLT">XSLT</a>, this is done as
a separate C library on top of libxml called libxslt, not released yet but
available from CVS</li>
<li>Finishing up <a href="http://www.w3.org/TR/xptr">XPointer</a> and <a
href="http://www.w3.org/TR/xinclude">XInclude</a></li>
<li>(seeems working but delayed from release) parsing/import of Docbook SGML
docs</li>
</ul>
<h3>2.3.8: May 3 2001</h3>
<ul>
<li>Integrated an SGML DocBook parser for the Gnome project</li>
<li>Fixed a few things in the HTML parser</li>
<li>Fixed some XPath bugs raised by XSLT use, tried to fix the floating
point portability issue</li>
<li>Speed improvement (8M/s for SAX, 3M/s for DOM, 1.5M/s for DOM+validation
using the XML REC as input and a 700MHz celeron).</li>
<li>incorporated more Windows cleanup</li>
<li>added xmlSaveFormatFile()</li>
<li>fixed problems in copying nodes with entities references (gdome)</li>
<li>removed some troubles surrounding the new validation module</li>
</ul>
<h3>2.3.7: April 22 2001</h3>
<ul>
<li>lots of small bug fixes, corrected XPointer</li>
<li>Non determinist content model validation support</li>
<li>added xmlDocCopyNode for gdome2</li>
<li>revamped the way the HTML parser handles end of tags</li>
<li>XPath: corrctions of namespacessupport and number formatting</li>
<li>Windows: Igor Zlatkovic patches for MSC compilation</li>
<li>HTML ouput fixes from P C Chow and William M. Brack</li>
<li>Improved validation speed sensible for DocBook</li>
<li>fixed a big bug with ID declared in external parsed entities</li>
<li>portability fixes, update of Trio from Bjorn Reese</li>
</ul>
<h3>2.3.6: April 8 2001</h3>
<ul>
<li>Code cleanup using extreme gcc compiler warning options, found and
cleared half a dozen potential problem</li>
<li>the Eazel team found an XML parser bug</li>
<li>cleaned up the user of some of the string formatting function. used the
trio library code to provide the one needed when the platform is missing
them</li>
<li>xpath: removed a memory leak and fixed the predicate evaluation problem,
extended the testsuite and cleaned up the result. XPointer seems broken
...</li>
</ul>
<h3>2.3.5: Mar 23 2001</h3>
<ul>
<li>Biggest change is separate parsing and evaluation of XPath expressions,
there is some new APIs for this too</li>
<li>included a number of bug fixes(XML push parser, 51876, notations,
52299)</li>
<li>Fixed some portability issues</li>
</ul>
<h3>2.3.4: Mar 10 2001</h3>
<ul>
<li>Fixed bugs #51860 and #51861</li>
<li>Added a global variable xmlDefaultBufferSize to allow default buffer
size to be application tunable.</li>
<li>Some cleanup in the validation code, still a bug left and this part
should probably be rewritten to support ambiguous content model :-\</li>
<li>Fix a couple of serious bugs introduced or raised by changes in 2.3.3
parser</li>
<li>Fixed another bug in xmlNodeGetContent()</li>
<li>Bjorn fixed XPath node collection and Number formatting</li>
<li>Fixed a loop reported in the HTML parsing</li>
<li>blank space are reported even if the Dtd content model proves that they
are formatting spaces, this is for XmL conformance</li>
</ul>
<h3>2.3.3: Mar 1 2001</h3>
<ul>
<li>small change in XPath for XSLT</li>
<li>documentation cleanups</li>
<li>fix in validation by Gary Pennington</li>
<li>serious parsing performances improvements</li>
</ul>
<h3>2.3.2: Feb 24 2001</h3>
<ul>
<li>chasing XPath bugs, found a bunch, completed some TODO</li>
<li>fixed a Dtd parsing bug</li>
<li>fixed a bug in xmlNodeGetContent</li>
<li>ID/IDREF support partly rewritten by Gary Pennington</li>
</ul>
<h3>2.3.1: Feb 15 2001</h3>
<ul>
<li>some XPath and HTML bug fixes for XSLT</li>
<li>small extension of the hash table interfaces for DOM gdome2
implementation</li>
<li>A few bug fixes</li>
</ul>
<h3>2.3.0: Feb 8 2001 (2.2.12 was on 25 Jan but I didn't kept track)</h3>
<ul>
<li>Lots of XPath bug fixes</li>
<li>Add a mode with Dtd lookup but without validation error reporting for
XSLT</li>
<li>Add support for text node without escaping (XSLT)</li>
<li>bug fixes for xmlCheckFilename</li>
<li>validation code bug fixes from Gary Pennington</li>
<li>Patch from Paul D. Smith correcting URI path normalization</li>
<li>Patch to allow simultaneous install of libxml-devel and
libxml2-devel</li>
<li>the example Makefile is now fixed</li>
<li>added HTML to the RPM packages</li>
<li>tree copying bugfixes</li>
<li>updates to Windows makefiles</li>
<li>optimisation patch from Bjorn Reese</li>
</ul>
<h3>2.2.11: Jan 4 2001</h3>
<ul>
<li>bunch of bug fixes (memory I/O, xpath, ftp/http, ...)</li>
<li>added htmlHandleOmittedElem()</li>
<li>Applied Bjorn Reese's IPV6 first patch</li>
<li>Applied Paul D. Smith patches for validation of XInclude results</li>
<li>added XPointer xmlns() new scheme support</li>
</ul>
<h3>2.2.10: Nov 25 2000</h3>
<ul>
<li>Fix the Windows problems of 2.2.8</li>
<li>integrate OpenVMS patches</li>
<li>better handling of some nasty HTML input</li>
<li>Improved the XPointer implementation</li>
<li>integrate a number of provided patches</li>
</ul>
<h3>2.2.9: Nov 25 2000</h3>
<ul>
<li>erroneous release :-(</li>
</ul>
<h3>2.2.8: Nov 13 2000</h3>
<ul>
<li>First version of <a href="http://www.w3.org/TR/xinclude">XInclude</a>
support</li>
<li>Patch in conditional section handling</li>
<li>updated MS compiler project</li>
<li>fixed some XPath problems</li>
<li>added an URI escaping function</li>
<li>some other bug fixes</li>
</ul>
<h3>2.2.7: Oct 31 2000</h3>
<ul>
<li>added message redirection</li>
<li>XPath improvements (thanks TOM !)</li>
<li>xmlIOParseDTD() added</li>
<li>various small fixes in the HTML, URI, HTTP and XPointer support</li>
<li>some cleanup of the Makefile, autoconf and the distribution content</li>
</ul>
<h3>2.2.6: Oct 25 2000:</h3>
<ul>
<li>Added an hash table module, migrated a number of internal structure to
those</li>
<li>Fixed a posteriori validation problems</li>
<li>HTTP module cleanups</li>
<li>HTML parser improvements (tag errors, script/style handling, attribute
normalization)</li>
<li>coalescing of adjacent text nodes</li>
<li>couple of XPath bug fixes, exported the internal API</li>
</ul>
<h3>2.2.5: Oct 15 2000:</h3>
<ul>
<li>XPointer implementation and testsuite</li>
<li>Lot of XPath fixes, added variable and functions registration, more
tests</li>
<li>Portability fixes, lots of enhancements toward an easy Windows build and
release</li>
<li>Late validation fixes</li>
<li>Integrated a lot of contributed patches</li>
<li>added memory management docs</li>
<li>a performance problem when using large buffer seems fixed</li>
</ul>
<h3>2.2.4: Oct 1 2000:</h3>
<ul>
<li>main XPath problem fixed</li>
<li>Integrated portability patches for Windows</li>
<li>Serious bug fixes on the URI and HTML code</li>
</ul>
<h3>2.2.3: Sep 17 2000</h3>
<ul>
<li>bug fixes</li>
<li>cleanup of entity handling code</li>
<li>overall review of all loops in the parsers, all sprintf usage has been
checked too</li>
<li>Far better handling of larges Dtd. Validating against Docbook XML Dtd
works smoothly now.</li>
</ul>
<h3>1.8.10: Sep 6 2000</h3>
<ul>
<li>bug fix release for some Gnome projects</li>
</ul>
<h3>2.2.2: August 12 2000</h3>
<ul>
<li>mostly bug fixes</li>
<li>started adding routines to access xml parser context options</li>
</ul>
<h3>2.2.1: July 21 2000</h3>
<ul>
<li>a purely bug fixes release</li>
<li>fixed an encoding support problem when parsing from a memory block</li>
<li>fixed a DOCTYPE parsing problem</li>
<li>removed a bug in the function allowing to override the memory allocation
routines</li>
</ul>
<h3>2.2.0: July 14 2000</h3>
<ul>
<li>applied a lot of portability fixes</li>
<li>better encoding support/cleanup and saving (content is now always
encoded in UTF-8)</li>
<li>the HTML parser now correctly handles encodings</li>
<li>added xmlHasProp()</li>
<li>fixed a serious problem with &amp;#38;</li>
<li>propagated the fix to FTP client</li>
<li>cleanup, bugfixes, etc ...</li>
<li>Added a page about <a href="encoding.html">libxml Internationalization
support</a></li>
</ul>
<h3>1.8.9: July 9 2000</h3>
<ul>
<li>fixed the spec the RPMs should be better</li>
<li>fixed a serious bug in the FTP implementation, released 1.8.9 to solve
rpmfind users problem</li>
</ul>
<h3>2.1.1: July 1 2000</h3>
<ul>
<li>fixes a couple of bugs in the 2.1.0 packaging</li>
<li>improvements on the HTML parser</li>
</ul>
<h3>2.1.0 and 1.8.8: June 29 2000</h3>
<ul>
<li>1.8.8 is mostly a comodity package for upgrading to libxml2 accoding to
<a href="upgrade.html">new instructions</a>. It fixes a nasty problem
about &amp;#38; charref parsing</li>
<li>2.1.0 also ease the upgrade from libxml v1 to the recent version. it
also contains numerous fixes and enhancements:
<ul>
<li>added xmlStopParser() to stop parsing</li>
<li>improved a lot parsing speed when there is large CDATA blocs</li>
<li>includes XPath patches provided by Picdar Technology</li>
<li>tried to fix as much as possible DtD validation and namespace
related problems</li>
<li>output to a given encoding has been added/tested</li>
<li>lot of various fixes</li>
</ul>
</li>
</ul>
<h3>2.0.0: Apr 12 2000</h3>
<ul>
<li>First public release of libxml2. If you are using libxml, it's a good
idea to check the 1.x to 2.x upgrade instructions. NOTE: while initally
scheduled for Apr 3 the relase occured only on Apr 12 due to massive
workload.</li>
<li>The include are now located under $prefix/include/libxml (instead of
$prefix/include/gnome-xml), they also are referenced by
<pre>#include &lt;libxml/xxx.h&gt;</pre>
<p>instead of</p>
<pre>#include "xxx.h"</pre>
</li>
<li>a new URI module for parsing URIs and following strictly RFC 2396</li>
<li>the memory allocation routines used by libxml can now be overloaded
dynamically by using xmlMemSetup()</li>
<li>The previously CVS only tool tester has been renamed
<strong>xmllint</strong> and is now installed as part of the libxml2
package</li>
<li>The I/O interface has been revamped. There is now ways to plug in
specific I/O modules, either at the URI scheme detection level using
xmlRegisterInputCallbacks() or by passing I/O functions when creating a
parser context using xmlCreateIOParserCtxt()</li>
<li>there is a C preprocessor macro LIBXML_VERSION providing the version
number of the libxml module in use</li>
<li>a number of optional features of libxml can now be excluded at configure
time (FTP/HTTP/HTML/XPath/Debug)</li>
</ul>
<h3>2.0.0beta: Mar 14 2000</h3>
<ul>
<li>This is a first Beta release of libxml version 2</li>
<li>It's available only from<a href="ftp://xmlsoft.org/">xmlsoft.org
FTP</a>, it's packaged as libxml2-2.0.0beta and available as tar and
RPMs</li>
<li>This version is now the head in the Gnome CVS base, the old one is
available under the tag LIB_XML_1_X</li>
<li>This includes a very large set of changes. Froma programmatic point of
view applications should not have to be modified too much, check the <a
href="upgrade.html">upgrade page</a></li>
<li>Some interfaces may changes (especially a bit about encoding).</li>
<li>the updates includes:
<ul>
<li>fix I18N support. ISO-Latin-x/UTF-8/UTF-16 (nearly) seems correctly
handled now</li>
<li>Better handling of entities, especially well formedness checking and
proper PEref extensions in external subsets</li>
<li>DTD conditional sections</li>
<li>Validation now correcly handle entities content</li>
<li><a href="http://rpmfind.net/tools/gdome/messages/0039.html">change
structures to accomodate DOM</a></li>
</ul>
</li>
<li>Serious progress were made toward compliance, <a
href="conf/result.html">here are the result of the test</a> against the
OASIS testsuite (except the japanese tests since I don't support that
encoding yet). This URL is rebuilt every couple of hours using the CVS
head version.</li>
</ul>
<h3>1.8.7: Mar 6 2000</h3>
<ul>
<li>This is a bug fix release:</li>
<li>It is possible to disable the ignorable blanks heuristic used by
libxml-1.x, a new function xmlKeepBlanksDefault(0) will allow this. Note
that for adherence to XML spec, this behaviour will be disabled by default
in 2.x . The same function will allow to keep compatibility for old
code.</li>
<li>Blanks in &lt;a&gt; &lt;/a&gt; constructs are not ignored anymore,
avoiding heuristic is really the Right Way :-\</li>
<li>The unchecked use of snprintf which was breaking libxml-1.8.6
compilation on some platforms has been fixed</li>
<li>nanoftp.c nanohttp.c: Fixed '#' and '?' stripping when processing
URIs</li>
</ul>
<h3>1.8.6: Jan 31 2000</h3>
<ul>
<li>added a nanoFTP transport module, debugged until the new version of <a
href="http://rpmfind.net/linux/rpm2html/rpmfind.html">rpmfind</a> can use
it without troubles</li>
</ul>
<h3>1.8.5: Jan 21 2000</h3>
<ul>
<li>adding APIs to parse a well balanced chunk of XML (production <a
href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the XML
spec)</li>
<li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li>
<li>Jody Goldberg &lt;jgoldberg@home.com&gt; provided another patch trying
to solve the zlib checks problems</li>
<li>The current state in gnome CVS base is expected to ship as 1.8.5 with
gnumeric soon</li>
</ul>
<h3>1.8.4: Jan 13 2000</h3>
<ul>
<li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li>
<li>all exit() call should have been removed from libxml</li>
<li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li>
<li>added newDocFragment()</li>
</ul>
<h3>1.8.3: Jan 5 2000</h3>
<ul>
<li>a Push interface for the XML and HTML parsers</li>
<li>a shell-like interface to the document tree (try tester --shell :-)</li>
<li>lots of bug fixes and improvement added over XMas hollidays</li>
<li>fixed the DTD parsing code to work with the xhtml DTD</li>
<li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li>
<li>Fixed bugs in xmlNewNs()</li>
<li>External entity loading code has been revamped, now it uses
xmlLoadExternalEntity(), some fix on entities processing were added</li>
<li>cleaned up WIN32 includes of socket stuff</li>
</ul>
<h3>1.8.2: Dec 21 1999</h3>
<ul>
<li>I got another problem with includes and C++, I hope this issue is fixed
for good this time</li>
<li>Added a few tree modification functions: xmlReplaceNode,
xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and
xmlDocSetRootElement</li>
<li>Tried to improve the HTML output with help from <a
href="mailto:clahey@umich.edu">Chris Lahey</a></li>
</ul>
<h3>1.8.1: Dec 18 1999</h3>
<ul>
<li>various patches to avoid troubles when using libxml with C++ compilers
the "namespace" keyword and C escaping in include files</li>
<li>a problem in one of the core macros IS_CHAR was corrected</li>
<li>fixed a bug introduced in 1.8.0 breaking default namespace processing,
and more specifically the Dia application</li>
<li>fixed a posteriori validation (validation after parsing, or by using a
Dtd not specified in the original document)</li>
<li>fixed a bug in</li>
</ul>
<h3>1.8.0: Dec 12 1999</h3>
<ul>
<li>cleanup, especially memory wise</li>
<li>the parser should be more reliable, especially the HTML one, it should
not crash, whatever the input !</li>
<li>Integrated various patches, especially a speedup improvement for large
dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>,
configure with --with-buffers to enable them.</li>
<li>attribute normalization, oops should have been added long ago !</li>
<li>attributes defaulted from Dtds should be available, xmlSetProp() now
does entities escapting by default.</li>
</ul>
<h3>1.7.4: Oct 25 1999</h3>
<ul>
<li>Lots of HTML improvement</li>
<li>Fixed some errors when saving both XML and HTML</li>
<li>More examples, the regression tests should now look clean</li>
<li>Fixed a bug with contiguous charref</li>
</ul>
<h3>1.7.3: Sep 29 1999</h3>
<ul>
<li>portability problems fixed</li>
<li>snprintf was used unconditionnally, leading to link problems on system
were it's not available, fixed</li>
</ul>
<h3>1.7.1: Sep 24 1999</h3>
<ul>
<li>The basic type for strings manipulated by libxml has been renamed in
1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason
is that CHAR was conflicting with a predefined type on Windows. However on
non WIN32 environment, compatibility is provided by the way of a
<strong>#define </strong>.</li>
<li>Changed another error : the use of a structure field called errno, and
leading to troubles on platforms where it's a macro</li>
</ul>
<h3>1.7.0: sep 23 1999</h3>
<ul>
<li>Added the ability to fetch remote DTD or parsed entities, see the <a
href="html/libxml-nanohttp.html">nanohttp</a> module.</li>
<li>Added an errno to report errors by another mean than a simple printf
like callback</li>
<li>Finished ID/IDREF support and checking when validation</li>
<li>Serious memory leaks fixed (there is now a <a
href="html/libxml-xmlmemory.html">memory wrapper</a> module)</li>
<li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a>
implementation</li>
<li>Added an HTML parser front-end</li>
</ul>
<h2><a name="XML">XML</a></h2>
<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for
markup-based structured documents. Here is <a name="example">an example XML
document</a>:</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;EXAMPLE prop1="gnome is great" prop2="&amp;amp; linux too"&gt;
&lt;head&gt;
&lt;title&gt;Welcome to Gnome&lt;/title&gt;
&lt;/head&gt;
&lt;chapter&gt;
&lt;title&gt;The Linux adventure&lt;/title&gt;
&lt;p&gt;bla bla bla ...&lt;/p&gt;
&lt;image href="linus.gif"/&gt;
&lt;p&gt;...&lt;/p&gt;
&lt;/chapter&gt;
&lt;/EXAMPLE&gt;</pre>
<p>The first line specifies that it's an XML document and gives useful
information about its encoding. Then the document is a text format whose
structure is specified by tags between brackets. <strong>Each tag opened has
to be closed</strong>. XML is pedantic about this. However, if a tag is empty
(no content), a single tag can serve as both the opening and closing tag if it
ends with <code>/&gt;</code> rather than with <code>&gt;</code>. Note that,
for example, the image tag has no content (just an attribute) and is closed by
ending the tag with <code>/&gt;</code>.</p>
<p>XML can be applied sucessfully to a wide range of uses, from long term
structured document maintenance (where it follows the steps of SGML) to simple
data encoding mechanisms like configuration file formatting (glade),
spreadsheets (gnumeric), or even shorter lived documents such as WebDAV where
it is used to encode remote calls between a client and a server.</p>
<h2><a name="XSLT">XSLT</a></h2>
<p>Check <a href="http://xmlsoft.org/XSLT">the separate libxslt page</a></p>
<p><a href="http://www.w3.org/TR/xslt">XSL Transformations</a>, is a language
for transforming XML documents into other XML documents (or HTML/textual
output).</p>
<p>A separate library called libxslt is being built on top of libxml2. This
module "libxslt" can be found in the Gnome CVS base too.</p>
<p>You can check the <a
href="http://cvs.gnome.org/lxr/source/libxslt/FEATURES">features</a> supported
and the progresses on the <a
href="http://cvs.gnome.org/lxr/source/libxslt/ChangeLog">Changelog</a></p>
<h2>An overview of libxml architecture</h2>
<p>Libxml is made of multiple components; some of them are optional, and most
of the block interfaces are public. The main components are:</p>
<ul>
<li>an Input/Output layer</li>
<li>FTP and HTTP client layers (optional)</li>
<li>an Internationalization layer managing the encodings support</li>
<li>a URI module</li>
<li>the XML parser and its basic SAX interface</li>
<li>an HTML parser using the same SAX interface (optional)</li>
<li>a SAX tree module to build an in-memory DOM representation</li>
<li>a tree module to manipulate the DOM representation</li>
<li>a validation module using the DOM representation (optional)</li>
<li>an XPath module for global lookup in a DOM representation
(optional)</li>
<li>a debug module (optional)</li>
</ul>
<p>Graphically this gives the following:</p>
<p><img src="libxml.gif" alt="a graphical view of the various"></p>
<p></p>
<h2><a name="tree">The tree output</a></h2>
<p>The parser returns a tree built during the document analysis. The value
returned is an <strong>xmlDocPtr</strong> (i.e., a pointer to an
<strong>xmlDoc</strong> structure). This structure contains information such
as the file name, the document type, and a <strong>children</strong> pointer
which is the root of the document (or more exactly the first child under the
root which is the document). The tree is made of <strong>xmlNode</strong>s,
chained in double-linked lists of siblings and with a children&lt;-&gt;parent
relationship. An xmlNode can also carry properties (a chain of xmlAttr
structures). An attribute may have a value which is a list of TEXT or
ENTITY_REF nodes.</p>
<p>Here is an example (erroneous with respect to the XML spec since there
should be only one ELEMENT under the root):</p>
<p><img src="structure.gif" alt=" structure.gif "></p>
<p>In the source package there is a small program (not installed by default)
called <strong>xmllint</strong> which parses XML files given as argument and
prints them back as parsed. This is useful for detecting errors both in XML
code and in the XML parser itself. It has an option <strong>--debug</strong>
which prints the actual in-memory structure of the document; here is the
result with the <a href="#example">example</a> given before:</p>
<pre>DOCUMENT
version=1.0
standalone=true
ELEMENT EXAMPLE
ATTRIBUTE prop1
TEXT
content=gnome is great
ATTRIBUTE prop2
ENTITY_REF
TEXT
content= linux too
ELEMENT head
ELEMENT title
TEXT
content=Welcome to Gnome
ELEMENT chapter
ELEMENT title
TEXT
content=The Linux adventure
ELEMENT p
TEXT
content=bla bla bla ...
ELEMENT image
ATTRIBUTE href
TEXT
content=linus.gif
ELEMENT p
TEXT
content=...</pre>
<p>This should be useful for learning the internal representation model.</p>
<h2><a name="interface">The SAX interface</a></h2>
<p>Sometimes the DOM tree output is just too large to fit reasonably into
memory. In that case (and if you don't expect to save back the XML document
loaded using libxml), it's better to use the SAX interface of libxml. SAX is a
<strong>callback-based interface</strong> to the parser. Before parsing, the
application layer registers a customized set of callbacks which are called by
the library as it progresses through the XML input.</p>
<p>To get more detailed step-by-step guidance on using the SAX interface of
libxml, see the <a
href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">nice
documentation</a>.written by <a href="mailto:james@daa.com.au">James
Henstridge</a>.</p>
<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
program located in the gnome-xml module (it's usually not shipped in the
binary packages of libxml, but you can find it in the tar source
distribution). Here is the sequence of callbacks that would be reported by
testSAX when parsing the example XML document shown earlier:</p>
<pre>SAX.setDocumentLocator()
SAX.startDocument()
SAX.getEntity(amp)
SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp;amp; linux too')
SAX.characters( , 3)
SAX.startElement(head)
SAX.characters( , 4)
SAX.startElement(title)
SAX.characters(Welcome to Gnome, 16)
SAX.endElement(title)
SAX.characters( , 3)
SAX.endElement(head)
SAX.characters( , 3)
SAX.startElement(chapter)
SAX.characters( , 4)
SAX.startElement(title)
SAX.characters(The Linux adventure, 19)
SAX.endElement(title)
SAX.characters( , 4)
SAX.startElement(p)
SAX.characters(bla bla bla ..., 15)
SAX.endElement(p)
SAX.characters( , 4)
SAX.startElement(image, href='linus.gif')
SAX.endElement(image)
SAX.characters( , 4)
SAX.startElement(p)
SAX.characters(..., 3)
SAX.endElement(p)
SAX.characters( , 3)
SAX.endElement(chapter)
SAX.characters( , 1)
SAX.endElement(EXAMPLE)
SAX.endDocument()</pre>
<p>Most of the other interfaces of libxml are based on the DOM tree-building
facility, so nearly everything up to the end of this document presupposes the
use of the standard DOM tree build. Note that the DOM tree itself is built by
a set of registered default callbacks, without internal specific
interface.</p>
<h2><a name="library">The XML library interfaces</a></h2>
<p>This section is directly intended to help programmers getting bootstrapped
using the XML library from the C language. It is not intended to be extensive.
I hope the automatically generated documents will provide the completeness
required, but as a separate set of documents. The interfaces of the XML
library are by principle low level, there is nearly zero abstraction. Those
interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are
separated from the <a href="html/libxml-htmlparser.html">HTML parser
interfaces</a>. Let's have a look at how the XML parser can be called:</p>
<h3><a name="Invoking">Invoking the parser : the pull method</a></h3>
<p>Usually, the first thing to do is to read an XML input. The parser accepts
documents either from in-memory strings or from files. The functions are
defined in "parser.h":</p>
<dl>
<dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
<dd><p>Parse a null-terminated string containing the document.</p>
</dd>
</dl>
<dl>
<dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
<dd><p>Parse an XML document contained in a (possibly compressed)
file.</p>
</dd>
</dl>
<p>The parser returns a pointer to the document structure (or NULL in case of
failure).</p>
<h3 id="Invoking1">Invoking the parser: the push method</h3>
<p>In order for the application to keep the control when the document is being
fetched (which is common for GUI based programs) libxml provides a push
interface, too, as of version 1.8.3. Here are the interface functions:</p>
<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
void *user_data,
const char *chunk,
int size,
const char *filename);
int xmlParseChunk (xmlParserCtxtPtr ctxt,
const char *chunk,
int size,
int terminate);</pre>
<p>and here is a simple example showing how to use the interface:</p>
<pre> FILE *f;
f = fopen(filename, "r");
if (f != NULL) {
int res, size = 1024;
char chars[1024];
xmlParserCtxtPtr ctxt;
res = fread(chars, 1, 4, f);
if (res &gt; 0) {
ctxt = xmlCreatePushParserCtxt(NULL, NULL,
chars, res, filename);
while ((res = fread(chars, 1, size, f)) &gt; 0) {
xmlParseChunk(ctxt, chars, res, 0);
}
xmlParseChunk(ctxt, chars, 0, 1);
doc = ctxt-&gt;myDoc;
xmlFreeParserCtxt(ctxt);
}
}</pre>
<p>The HTML parser embedded into libxml also has a push interface; the
functions are just prefixed by "html" rather than "xml".</p>
<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
<p>The tree-building interface makes the parser memory-hungry, first loading
the document in memory and then building the tree itself. Reading a document
without building the tree is possible using the SAX interfaces (see SAX.h and
<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
Henstridge's documentation</a>). Note also that the push interface can be
limited to SAX: just use the two first arguments of
<code>xmlCreatePushParserCtxt()</code>.</p>
<h3><a name="Building">Building a tree from scratch</a></h3>
<p>The other way to get an XML tree in memory is by building it. Basically
there is a set of functions dedicated to building new elements. (These are
also described in &lt;libxml/tree.h&gt;.) For example, here is a piece of code
that produces the XML document used in the previous examples:</p>
<pre> #include &lt;libxml/tree.h&gt;
xmlDocPtr doc;
xmlNodePtr tree, subtree;
doc = xmlNewDoc("1.0");
doc-&gt;children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
xmlSetProp(doc-&gt;children, "prop1", "gnome is great");
xmlSetProp(doc-&gt;children, "prop2", "&amp; linux too");
tree = xmlNewChild(doc-&gt;children, NULL, "head", NULL);
subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
tree = xmlNewChild(doc-&gt;children, NULL, "chapter", NULL);
subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
subtree = xmlNewChild(tree, NULL, "image", NULL);
xmlSetProp(subtree, "href", "linus.gif");</pre>
<p>Not really rocket science ...</p>
<h3><a name="Traversing">Traversing the tree</a></h3>
<p>Basically by <a href="html/libxml-tree.html">including "tree.h"</a> your
code has access to the internal structure of all the elements of the tree. The
names should be somewhat simple like <strong>parent</strong>,
<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>,
<strong>properties</strong>, etc... For example, still with the previous
example:</p>
<pre><code>doc-&gt;children-&gt;children-&gt;children</code></pre>
<p>points to the title element,</p>
<pre>doc-&gt;children-&gt;children-&gt;next-&gt;children-&gt;children</pre>
<p>points to the text node containing the chapter title "The Linux
adventure".</p>
<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
present before the document root, so <code>doc-&gt;children</code> may point
to an element which is not the document Root Element; a function
<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
<h3><a name="Modifying">Modifying the tree</a></h3>
<p>Functions are provided for reading and writing the document content. Here
is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p>
<dl>
<dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
xmlChar *value);</code></dt>
<dd><p>This sets (or changes) an attribute carried by an ELEMENT node. The
value can be NULL.</p>
</dd>
</dl>
<dl>
<dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
*name);</code></dt>
<dd><p>This function returns a pointer to new copy of the property
content. Note that the user must deallocate the result.</p>
</dd>
</dl>
<p>Two functions are provided for reading and writing the text associated with
elements:</p>
<dl>
<dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
*value);</code></dt>
<dd><p>This function takes an "external" string and converts it to one
text node or possibly to a list of entity and text nodes. All
non-predefined entity references like &amp;Gnome; will be stored
internally as entity nodes, hence the result of the function may not be
a single node.</p>
</dd>
</dl>
<dl>
<dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
inLine);</code></dt>
<dd><p>This function is the inverse of
<code>xmlStringGetNodeList()</code>. It generates a new string
containing the content of the text and entity nodes. Note the extra
argument inLine. If this argument is set to 1, the function will expand
entity references. For example, instead of returning the &amp;Gnome;
XML encoding in the string, it will substitute it with its value (say,
"GNU Network Object Model Environment").</p>
</dd>
</dl>
<h3><a name="Saving">Saving a tree</a></h3>
<p>Basically 3 options are possible:</p>
<dl>
<dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
*size);</code></dt>
<dd><p>Returns a buffer into which the document has been saved.</p>
</dd>
</dl>
<dl>
<dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
<dd><p>Dumps a document to an open file descriptor.</p>
</dd>
</dl>
<dl>
<dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
<dd><p>Saves the document to a file. In this case, the compression
interface is triggered if it has been turned on.</p>
</dd>
</dl>
<h3><a name="Compressio">Compression</a></h3>
<p>The library transparently handles compression when doing file-based
accesses. The level of compression on saves can be turned on either globally
or individually for one file:</p>
<dl>
<dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
<dd><p>Gets the document compression ratio (0-9).</p>
</dd>
</dl>
<dl>
<dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
<dd><p>Sets the document compression ratio.</p>
</dd>
</dl>
<dl>
<dt><code>int xmlGetCompressMode(void);</code></dt>
<dd><p>Gets the default compression ratio.</p>
</dd>
</dl>
<dl>
<dt><code>void xmlSetCompressMode(int mode);</code></dt>
<dd><p>Sets the default compression ratio.</p>
</dd>
</dl>
<h2><a name="Entities">Entities or no entities</a></h2>
<p>Entities in principle are similar to simple C macros. An entity defines an
abbreviation for a given string that you can reuse many times throughout the
content of your document. Entities are especially useful when a given string
may occur frequently within a document, or to confine the change needed to a
document to a restricted area in the internal subset of the document (at the
beginning). Example:</p>
<pre>1 &lt;?xml version="1.0"?&gt;
2 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
3 &lt;!ENTITY xml "Extensible Markup Language"&gt;
4 ]&gt;
5 &lt;EXAMPLE&gt;
6 &amp;xml;
7 &lt;/EXAMPLE&gt;</pre>
<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing
its name with '&amp;' and following it by ';' without any spaces added. There
are 5 predefined entities in libxml allowing you to escape charaters with
predefined meaning in some parts of the xml document content:
<strong>&amp;lt;</strong> for the character '&lt;', <strong>&amp;gt;</strong>
for the character '&gt;', <strong>&amp;apos;</strong> for the character ''',
<strong>&amp;quot;</strong> for the character '"', and
<strong>&amp;amp;</strong> for the character '&amp;'.</p>
<p>One of the problems related to entities is that you may want the parser to
substitute an entity's content so that you can see the replacement text in
your application. Or you may prefer to keep entity references as such in the
content to be able to save the document back without losing this usually
precious information (if the user went through the pain of explicitly defining
entities, he may have a a rather negative attitude if you blindly susbtitute
them as saving time). The <a
href="html/libxml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
function allows you to check and change the behaviour, which is to not
substitute entities by default.</p>
<p>Here is the DOM tree built by libxml for the previous document in the
default case:</p>
<pre>/gnome/src/gnome-xml -&gt; ./xmllint --debug test/ent1
DOCUMENT
version=1.0
ELEMENT EXAMPLE
TEXT
content=
ENTITY_REF
INTERNAL_GENERAL_ENTITY xml
content=Extensible Markup Language
TEXT
content=</pre>
<p>And here is the result when substituting entities:</p>
<pre>/gnome/src/gnome-xml -&gt; ./tester --debug --noent test/ent1
DOCUMENT
version=1.0
ELEMENT EXAMPLE
TEXT
content= Extensible Markup Language</pre>
<p>So, entities or no entities? Basically, it depends on your use case. I
suggest that you keep the non-substituting default behaviour and avoid using
entities in your XML document or data if you are not willing to handle the
entity references elements in the DOM tree.</p>
<p>Note that at save time libxml enforces the conversion of the predefined
entities where necessary to prevent well-formedness problems, and will also
transparently replace those with chars (i.e. it will not generate entity
reference elements in the DOM tree or call the reference() SAX callback when
finding them in the input).</p>
<p><span style="background-color: #FF0000">WARNING</span>: handling entities
on top of the libxml SAX interface is difficult!!! If you plan to use
non-predefined entities in your documents, then the learning cuvre to handle
then using the SAX API may be long. If you plan to use complex documents, I
strongly suggest you consider using the DOM interface instead and let libxml
deal with the complexity rather than trying to do it yourself.</p>
<h2><a name="Namespaces">Namespaces</a></h2>
<p>The libxml library implements <a
href="http://www.w3.org/TR/REC-xml-names/">XML namespaces</a> support by
recognizing namespace contructs in the input, and does namespace lookup
automatically when building the DOM tree. A namespace declaration is
associated with an in-memory structure and all elements or attributes within
that namespace point to it. Hence testing the namespace is a simple and fast
equality operation at the user level.</p>
<p>I suggest that people using libxml use a namespace, and declare it in the
root element of their document as the default namespace. Then they don't need
to use the prefix in the content but we will have a basis for future semantic
refinement and merging of data from different sources. This doesn't increase
the size of the XML output significantly, but significantly increases its
value in the long-term. Example:</p>
<pre>&lt;mydoc xmlns="http://mydoc.example.org/schemas/"&gt;
&lt;elem1&gt;...&lt;/elem1&gt;
&lt;elem2&gt;...&lt;/elem2&gt;
&lt;/mydoc&gt;</pre>
<p>The namespace value has to be an absolute URL, but the URL doesn't have to
point to any existing resource on the Web. It will bind all the element and
atributes with that URL. I suggest to use an URL within a domain you control,
and that the URL should contain some kind of version information if possible.
For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a good
namespace scheme.</p>
<p>Then when you load a file, make sure that a namespace carrying the
version-independent prefix is installed on the root element of your document,
and if the version information don't match something you know, warn the user
and be liberal in what you accept as the input. Also do *not* try to base
namespace checking on the prefix value. &lt;foo:text&gt; may be exactly the
same as &lt;bar:text&gt; in another document. What really matters is the URI
associated with the element or the attribute, not the prefix string (which is
just a shortcut for the full URI). In libxml, element and attributes have an
<code>ns</code> field pointing to an xmlNs structure detailing the namespace
prefix and its URI.</p>
<p>@@Interfaces@@</p>
<p>@@Examples@@</p>
<p>Usually people object to using namespaces together with validity checking.
I will try to make sure that using namespaces won't break validity checking,
so even if you plan to use or currently are using validation I strongly
suggest adding namespaces to your document. A default namespace scheme
<code>xmlns="http://...."</code> should not break validity even on less
flexible parsers. Using namespaces to mix and differentiate content coming
from multiple DTDs will certainly break current validation schemes. I will try
to provide ways to do this, but this may not be portable or standardized.</p>
<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
<p>Well what is validation and what is a DTD ?</p>
<p>Validation is the process of checking a document against a set of
construction rules; a <strong>DTD</strong> (Document Type Definition) is such
a set of rules.</p>
<p>The validation process and building DTDs are the two most difficult parts
of the XML life cycle. Briefly a DTD defines all the possibles element to be
found within your document, what is the formal shape of your document tree (by
defining the allowed content of an element, either text, a regular expression
for the allowed list of children, or mixed content i.e. both text and
children). The DTD also defines the allowed attributes for all elements and
the types of the attributes. For more detailed information, I suggest that you
read the related parts of the XML specification, the examples found under
gnome-xml/test/valid/dtd and any of the large number of books available on
XML. The dia example in gnome-xml/test/valid should be both simple and
complete enough to allow you to build your own.</p>
<p>A word of warning, building a good DTD which will fit the needs of your
application in the long-term is far from trivial; however, the extra level of
quality it can ensure is well worth the price for some sets of applications or
if you already have already a DTD defined for your application field.</p>
<p>The validation is not completely finished but in a (very IMHO) usable
state. Until a real validation interface is defined the way to do it is to
define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external
variable to 1, this will of course be changed at some point:</p>
<p>extern int xmlDoValidityCheckingDefaultValue;</p>
<p>...</p>
<p>xmlDoValidityCheckingDefaultValue = 1;</p>
<p></p>
<p>To handle external entities, use the function
<strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to
link in you HTTP/FTP/Entities database library to the standard libxml
core.</p>
<p>@@interfaces@@</p>
<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2>
<p><a href="http://www.w3.org/DOM/">DOM</a> stands for the <em>Document Object
Model</em>; this is an API for accessing XML or HTML structured documents.
Native support for DOM in Gnome is on the way (module gnome-dom), and will be
based on gnome-xml. This will be a far cleaner interface to manipulate XML
files within Gnome since it won't expose the internal structure.</p>
<p>The current DOM implementation on top of libxml is the <a
href="http://cvs.gnome.org/lxr/source/gdome2/">gdome2 Gnome module</a>, this
is a full DOM interface, thanks to Paolo Casarini, check the <a
href="http://www.cs.unibo.it/~casarini/gdome2/">Gdome2 homepage</a> for more
informations.</p>
<p>The gnome-dom and gdome modules in the Gnome CVS base are obsolete</p>
<h2><a name="Example"></a><a name="real">A real example</a></h2>
<p>Here is a real size example, where the actual content of the application
data is not kept in the DOM tree but uses internal structures. It is based on
a proposal to keep a database of jobs related to Gnome, with an XML based
storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
base</a>:</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location"&gt;
&lt;gjob:Jobs&gt;
&lt;gjob:Job&gt;
&lt;gjob:Project ID="3"/&gt;
&lt;gjob:Application&gt;GBackup&lt;/gjob:Application&gt;
&lt;gjob:Category&gt;Development&lt;/gjob:Category&gt;
&lt;gjob:Update&gt;
&lt;gjob:Status&gt;Open&lt;/gjob:Status&gt;
&lt;gjob:Modified&gt;Mon, 07 Jun 1999 20:27:45 -0400 MET DST&lt;/gjob:Modified&gt;
&lt;gjob:Salary&gt;USD 0.00&lt;/gjob:Salary&gt;
&lt;/gjob:Update&gt;
&lt;gjob:Developers&gt;
&lt;gjob:Developer&gt;
&lt;/gjob:Developer&gt;
&lt;/gjob:Developers&gt;
&lt;gjob:Contact&gt;
&lt;gjob:Person&gt;Nathan Clemons&lt;/gjob:Person&gt;
&lt;gjob:Email&gt;nathan@windsofstorm.net&lt;/gjob:Email&gt;
&lt;gjob:Company&gt;
&lt;/gjob:Company&gt;
&lt;gjob:Organisation&gt;
&lt;/gjob:Organisation&gt;
&lt;gjob:Webpage&gt;
&lt;/gjob:Webpage&gt;
&lt;gjob:Snailmail&gt;
&lt;/gjob:Snailmail&gt;
&lt;gjob:Phone&gt;
&lt;/gjob:Phone&gt;
&lt;/gjob:Contact&gt;
&lt;gjob:Requirements&gt;
The program should be released as free software, under the GPL.
&lt;/gjob:Requirements&gt;
&lt;gjob:Skills&gt;
&lt;/gjob:Skills&gt;
&lt;gjob:Details&gt;
A GNOME based system that will allow a superuser to configure
compressed and uncompressed files and/or file systems to be backed
up with a supported media in the system. This should be able to
perform via find commands generating a list of files that are passed
to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
or via operations performed on the filesystem itself. Email
notification and GUI status display very important.
&lt;/gjob:Details&gt;
&lt;/gjob:Job&gt;
&lt;/gjob:Jobs&gt;
&lt;/gjob:Helping&gt;</pre>
<p>While loading the XML file into an internal DOM tree is a matter of calling
only a couple of functions, browsing the tree to gather the ata and generate
the internal structures is harder, and more error prone.</p>
<p>The suggested principle is to be tolerant with respect to the input
structure. For example, the ordering of the attributes is not significant, the
XML specification is clear about it. It's also usually a good idea not to
depend on the order of the children of a given node, unless it really makes
things harder. Here is some code to parse the information for a person:</p>
<pre>/*
* A person record
*/
typedef struct person {
char *name;
char *email;
char *company;
char *organisation;
char *smail;
char *webPage;
char *phone;
} person, *personPtr;
/*
* And the code needed to parse it
*/
personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
personPtr ret = NULL;
DEBUG("parsePerson\n");
/*
* allocate the struct
*/
ret = (personPtr) malloc(sizeof(person));
if (ret == NULL) {
fprintf(stderr,"out of memory\n");
return(NULL);
}
memset(ret, 0, sizeof(person));
/* We don't care what the top level element name is */
cur = cur-&gt;xmlChildrenNode;
while (cur != NULL) {
if ((!strcmp(cur-&gt;name, "Person")) &amp;&amp; (cur-&gt;ns == ns))
ret-&gt;name = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
if ((!strcmp(cur-&gt;name, "Email")) &amp;&amp; (cur-&gt;ns == ns))
ret-&gt;email = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
cur = cur-&gt;next;
}
return(ret);
}</pre>
<p>Here are a couple of things to notice:</p>
<ul>
<li>Usually a recursive parsing style is the more convenient one: XML data
is by nature subject to repetitive constructs and usually exibits highly
stuctured patterns.</li>
<li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e.
the pointer to the global XML document and the namespace reserved to the
application. Document wide information are needed for example to decode
entities and it's a good coding practice to define a namespace for your
application set of data and test that the element and attributes you're
analyzing actually pertains to your application space. This is done by a
simple equality test (cur-&gt;ns == ns).</li>
<li>To retrieve text and attributes value, you can use the function
<em>xmlNodeListGetString</em> to gather all the text and entity reference
nodes generated by the DOM output and produce an single text string.</li>
</ul>
<p>Here is another piece of code used to parse another level of the
structure:</p>
<pre>#include &lt;libxml/tree.h&gt;
/*
* a Description for a Job
*/
typedef struct job {
char *projectID;
char *application;
char *category;
personPtr contact;
int nbDevelopers;
personPtr developers[100]; /* using dynamic alloc is left as an exercise */
} job, *jobPtr;
/*
* And the code needed to parse it
*/
jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
jobPtr ret = NULL;
DEBUG("parseJob\n");
/*
* allocate the struct
*/
ret = (jobPtr) malloc(sizeof(job));
if (ret == NULL) {
fprintf(stderr,"out of memory\n");
return(NULL);
}
memset(ret, 0, sizeof(job));
/* We don't care what the top level element name is */
cur = cur-&gt;xmlChildrenNode;
while (cur != NULL) {
if ((!strcmp(cur-&gt;name, "Project")) &amp;&amp; (cur-&gt;ns == ns)) {
ret-&gt;projectID = xmlGetProp(cur, "ID");
if (ret-&gt;projectID == NULL) {
fprintf(stderr, "Project has no ID\n");
}
}
if ((!strcmp(cur-&gt;name, "Application")) &amp;&amp; (cur-&gt;ns == ns))
ret-&gt;application = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
if ((!strcmp(cur-&gt;name, "Category")) &amp;&amp; (cur-&gt;ns == ns))
ret-&gt;category = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
if ((!strcmp(cur-&gt;name, "Contact")) &amp;&amp; (cur-&gt;ns == ns))
ret-&gt;contact = parsePerson(doc, ns, cur);
cur = cur-&gt;next;
}
return(ret);
}</pre>
<p>Once you are used to it, writing this kind of code is quite simple, but
boring. Ultimately, it could be possble to write stubbers taking either C data
structure definitions, a set of XML examples or an XML DTD and produce the
code needed to import and export the content between C data and XML storage.
This is left as an exercise to the reader :-)</p>
<p>Feel free to use <a href="example/gjobread.c">the code for the full C
parsing example</a> as a template, it is also available with Makefile in the
Gnome CVS base under gnome-xml/example</p>
<h2><a name="Contributi">Contributions</a></h2>
<ul>
<li><a href="mailto:ari@lusis.org">Ari Johnson</a> provides a C++ wrapper
for libxml:
<p>Website: <a
href="http://lusis.org/~ari/xml++/">http://lusis.org/~ari/xml++/</a></p>
<p>Download: <a
href="http://lusis.org/~ari/xml++/libxml++.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a></p>
</li>
<li><a href="mailto:doolin@cs.utk.edu">David Doolin</a> provides a
precompiled Windows version
<p><a
href="http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/">http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/</a></p>
</li>
<li><a
href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt
Sergeant</a> developped <a
href="http://axkit.org/download/">XML::LibXSLT</a>, a perl wrapper for
libxml2/libxslt as part of the <a href="http://axkit.com/">AxKit XML
application server</a></li>
<li><a href="mailto:fnatter@gmx.net">Felix Natter</a> provided <a
href="libxml-doc.el">an emacs module</a> to lookup libxml functions
documentation</li>
<li><a href="mailto:sherwin@nlm.nih.gov">Ziying Sherwin</a> provided <a
href="http://xmlsoft.org/messages/0488.html">man pages</a> (not yet
integrated in the distribution)</li>
</ul>
<p></p>
<p><a href="mailto:Daniel.Veillard@imag.fr">Daniel Veillard</a></p>
<p>$Id: xml.html,v 1.81 2001/04/22 19:31:17 veillard Exp $</p>
</body>
</html>