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blob: 7c2ac596c9bcfd0e9119be8e0a6ae92a635a442e [file] [log] [blame]
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]2 "http://www.w3.org/TR/REC-html40/loose.dtd">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]3<html>
4<head>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]5 <title>The XML library for Gnome</title>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]6 <meta name="GENERATOR" content="amaya V2.4">
7 <meta http-equiv="Content-Type" content="text/html">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]8</head>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]9
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]10<body bgcolor="#ffffff">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]11<h1 align="center">The XML library for Gnome</h1>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]12
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]13<h2 style="text-align: center">libxml, a.k.a. gnome-xml</h2>
14
15<p></p>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]16<ul>
17 <li><a href="#Introducti">Introduction</a></li>
18 <li><a href="#Documentat">Documentation</a></li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]19 <li><a href="#Downloads">Downloads</a></li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]20 <li><a href="#News">News</a></li>
21 <li><a href="#XML">XML</a></li>
22 <li><a href="#tree">The tree output</a></li>
23 <li><a href="#interface">The SAX interface</a></li>
24 <li><a href="#library">The XML library interfaces</a>
25 <ul>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]26 <li><a href="#Invoking">Invoking the parser: the pull way</a></li>
27 <li><a href="#Invoking">Invoking the parser: the push way</a></li>
28 <li><a href="#Invoking2">Invoking the parser: the SAX interface</a></li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]29 <li><a href="#Building">Building a tree from scratch</a></li>
30 <li><a href="#Traversing">Traversing the tree</a></li>
31 <li><a href="#Modifying">Modifying the tree</a></li>
32 <li><a href="#Saving">Saving the tree</a></li>
33 <li><a href="#Compressio">Compression</a></li>
34 </ul>
35 </li>
36 <li><a href="#Entities">Entities or no entities</a></li>
37 <li><a href="#Namespaces">Namespaces</a></li>
38 <li><a href="#Validation">Validation</a></li>
39 <li><a href="#Principles">DOM principles</a></li>
40 <li><a href="#real">A real example</a></li>
41</ul>
42
43<h2><a name="Introducti">Introduction</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]44
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]45<p>This document describes the <a href="http://www.w3.org/XML/">XML</a>
46library provideed in the <a href="http://www.gnome.org/">Gnome</a> framework.
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]47XML is a standard to build tag based structured documents/data.</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]48
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]49<p>Here are some key points about libxml:</p>
50<ul>
51 <li>The internal document repesentation is as close as possible to the <a
52 href="http://www.w3.org/DOM/">DOM</a> interfaces.</li>
53 <li>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX
54 like interface</a>, the interface is designed to be compatible with <a
55 href="http://www.jclark.com/xml/expat.html">Expat</a> one.</li>
56 <li>Libxml now include a nearly complete <a
57 href="http://www.w3.org/TR/xpath">XPath</a> implementation.</li>
58 <li>Libxml export Push and Pull type parser interface for both XML and
59 HTML.</li>
60 <li>This library is released both under the W3C Copyright and the GNU LGPL,
61 basically everybody should be happy, if not, drop me a mail.</li>
62</ul>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]63
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]64<h2><a name="Documentat">Documentation</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]65
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]66<p>There is some on-line resources about using libxml :</p>
67<ol>
68 <li>The code is commented in a way which allow <a
69 href="http://xmlsoft.org/libxml.html">extensive documentation</a> to be
70 automatically extracted.</li>
71 <li>This page provides a global overview and <a href="#real">some
72 examples</a> on how to use libxml</li>
73 <li><a href="mailto:james@daa.com.au">James Henstridge</a> made <a
74 href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice
75 documentation</a> expaining how to use the SAX interface of libxml</li>
76 <li>George Lebl wrote <a
77 href="http://www-4.ibm.com/software/developer/library/gnome3/">an article
78 for IBM developperWorks</a> about using libxml</li>
79 <li>It is also a good idea to check to <a href="mailto:raph@levien.com">Raph
80 Levien</a> <a href="http://levien.com/gnome/">web site</a> since he is
81 building the <a href="http://levien.com/gnome/gdome.html">DOM interface
82 gdome</a> on top of libxml result tree and an implementation of <a
83 href="http://www.w3.org/Graphics/SVG/">SVG</a> called <a
84 href="http://www.levien.com/svg/">gill</a>. Check his <a
85 href="http://www.levien.com/gnome/domination.html">DOMination
86 paper</a>.</li>
87 <li>And don't forget to look at the <a href="/messages/">mailing-list
88 archive</a> too.</li>
89</ol>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]90
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]91<h3>Reporting bugs and getting help</h3>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]92
93<p>Well bugs or missing features are always possible, and I will make a point
94of fixing them in a timely fashion. The best way it to <a
95href="http://bugs.gnome.org/db/pa/lgnome-xml.html">use the Gnome bug tracking
96database</a>. I look at reports there regulary and it's good to have a
97reminder when a bug is still open. Check the <a
98href="http://bugs.gnome.org/Reporting.html">instructions on reporting bugs</a>
99and be sure to specify thatthe bug is for the package gnome-xml.</p>
100
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]101<p>There is also a mailing-list <a
102href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> for libxml, with an <a
103href="http://xmlsoft.org/messages">on-line archive</a>. To subscribe to this
104majordomo based list, send a mail to <a
105href="mailto:majordomo@rufus.w3.org">majordomo@rufus.w3.org</a> with
106"subscribe xml" in the <strong>content</strong> of the message.</p>
107
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]108<p>Alternately you can just send the bug to the <a
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]109href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> list.</p>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]110
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]111<h2><a name="Downloads">Downloads</a></h2>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]112
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]113<p>Latest versions can be found on <a
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]114href="ftp://rpmfind.net/pub/veillard/">rpmfind.net</a> or on the <a
115href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]116as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]117archive</a> or <a href="ftp://ftp.gnome.org/pub/GNOME/contrib/rpms/">RPMs
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]118packages</a> (NOTE that you need both the <a
119href="http://rpmfind.net/linux/RPM/libxml.html">libxml</a> and <a
120href="http://rpmfind.net/linux/RPM/libxml-devel.html">libxml-devel</a>
121packages installed to compile applications using libxml).</p>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]122
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]123<p>Libxml is also available from 2 CVs bases:</p>
124<ul>
125 <li><p>The <a href="http://dev.w3.org/cvsweb/XML/">W3C CVS base</a>,
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]126 available read-only using the CVS pserver authentification (I tend to use
127 this base for my own developements so it's updated more regulary, but
128 content may not be as stable):</p>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]129 <pre>CVSROOT=:pserver:anonymous@dev.w3.org:/sources/public
130password: anonymous
131module: XML</pre>
132 </li>
133 <li><p>The <a
134 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&amp;dir=gnome-xml">Gnome
135 CVS base</a>, Check the <a
136 href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> page,
137 the CVS module is <b>gnome-xml</b></p>
138 </li>
139</ul>
140
141<h2><a name="News">News</a></h2>
142
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]143<h3>CVS only : check the <a
144href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file
145for really accurate description</h3>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]146<ul>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]147 <li>working on HTML and XML links recognition layers, get in touch with me
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]148 if you want to test those.</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]149 <li>adding APIs to parse a well balanced chunk of XML (production <a
150 href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the XML
151 spec)</li>
Daniel Veillard461a66c2000-01-18 18:01:01 +0000[diff] [blame^]152 <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li>
153 <li>Jody Goldberg &lt;jgoldberg@home.com> provided another patch trying to
154 solve the zlib checks problems</li>
155 <li>The current state in gnome CVS base is expected to ship as 1.8.5 with
156 gnumeric soon</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]157</ul>
158
159<h3>1.8.4: Jan 13 2000</h3>
160<ul>
161 <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li>
162 <li>all exit() call should have been removed from libxml</li>
163 <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li>
164 <li>added newDocFragment()</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]165</ul>
166
167<h3>1.8.3: Jan 5 2000</h3>
168<ul>
169 <li>a Push interface for the XML and HTML parsers</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]170 <li>an shell like interface to the document tree (try tester --shell
171 :-)</li>
Daniel Veillarddbfd6411999-12-28 16:35:14 +0000[diff] [blame]172 <li>lots of bug fixes and improvement added over XMas hollidays</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]173 <li>fixed the DTD parsing code to work with the xhtml DTD</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]174 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li>
175 <li>Fixed bugs in xmlNewNs()</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]176 <li>External entity loading code has been revamped, now it uses
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]177 xmlLoadExternalEntity(), some fix on entities processing were added</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]178 <li>cleaned up WIN32 includes of socket stuff</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]179</ul>
180
181<h3>1.8.2: Dec 21 1999</h3>
182<ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]183 <li>I got another problem with includes and C++, I hope this issue is fixed
184 for good this time</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]185 <li>Added a few tree modification functions: xmlReplaceNode,
186 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and
187 xmlDocSetRootElement</li>
188 <li>Tried to improve the HTML output with help from <a
189 href="mailto:clahey@umich.edu">Chris Lahey</a></li>
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]190</ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]191
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]192<h3>1.8.1: Dec 18 1999</h3>
193<ul>
194 <li>various patches to avoid troubles when using libxml with C++ compilers
195 the "namespace" keyword and C escaping in include files</li>
196 <li>a problem in one of the core macros IS_CHAR was corrected</li>
197 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing,
198 and more specifically the Dia application</li>
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]199 <li>fixed a posteriori validation (validation after parsing, or by using a
200 Dtd not specified in the original document)</li>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]201 <li>fixed a bug in</li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]202</ul>
203
204<h3>1.8.0: Dec 12 1999</h3>
205<ul>
206 <li>cleanup, especially memory wise</li>
207 <li>the parser should be more reliable, especially the HTML one, it should
208 not crash, whatever the input !</li>
209 <li>Integrated various patches, especially a speedup improvement for large
210 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>,
211 configure with --with-buffers to enable them.</li>
212 <li>attribute normalization, oops should have been added long ago !</li>
213 <li>attributes defaulted from Dtds should be available, xmlSetProp() now
214 does entities escapting by default.</li>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]215</ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]216
217<h3>1.7.4: Oct 25 1999</h3>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]218<ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]219 <li>Lots of HTML improvement</li>
220 <li>Fixed some errors when saving both XML and HTML</li>
221 <li>More examples, the regression tests should now look clean</li>
222 <li>Fixed a bug with contiguous charref</li>
223</ul>
224
225<h3>1.7.3: Sep 29 1999</h3>
226<ul>
227 <li>portability problems fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]228 <li>snprintf was used unconditionnally, leading to link problems on system
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]229 were it's not available, fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]230</ul>
231
232<h3>1.7.1: Sep 24 1999</h3>
233<ul>
234 <li>The basic type for strings manipulated by libxml has been renamed in
235 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason
236 is that CHAR was conflicting with a predefined type on Windows. However on
237 non WIN32 environment, compatibility is provided by the way of a
238 <strong>#define </strong>.</li>
239 <li>Changed another error : the use of a structure field called errno, and
240 leading to troubles on platforms where it's a macro</li>
241</ul>
242
243<h3>1.7.0: sep 23 1999</h3>
244<ul>
245 <li>Added the ability to fetch remote DTD or parsed entities, see the <a
246 href="gnome-xml-nanohttp.html">nanohttp</a> module.</li>
247 <li>Added an errno to report errors by another mean than a simple printf
248 like callback</li>
249 <li>Finished ID/IDREF support and checking when validation</li>
250 <li>Serious memory leaks fixed (there is now a <a
251 href="gnome-xml-xmlmemory.html">memory wrapper</a> module)</li>
252 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a>
253 implementation</li>
254 <li>Added an HTML parser front-end</li>
255</ul>
256
257<h2><a name="XML">XML</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]258
259<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for markup
260based structured documents, here is <a name="example">an example</a>:</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]261<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]262&lt;EXAMPLE prop1="gnome is great" prop2="&amp;amp; linux too">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]263 &lt;head>
264 &lt;title>Welcome to Gnome&lt;/title>
265 &lt;/head>
266 &lt;chapter>
267 &lt;title>The Linux adventure&lt;/title>
268 &lt;p>bla bla bla ...&lt;/p>
269 &lt;image href="linus.gif"/>
270 &lt;p>...&lt;/p>
271 &lt;/chapter>
272&lt;/EXAMPLE></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]273
274<p>The first line specify that it's an XML document and gives useful
275informations about it's encoding. Then the document is a text format whose
276structure is specified by tags between brackets. <strong>Each tag opened have
277to be closed</strong> XML is pedantic about this, not that for example the
278image tag has no content (just an attribute) and is closed by ending up the
279tag with <code>/></code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]280
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]281<p>XML can be applied sucessfully to a wide range or usage from long term
282structured document maintenance where it follows the steps of SGML to simple
283data encoding mechanism like configuration file format (glade), spreadsheets
284(gnumeric), or even shorter lived document like in WebDAV where it is used to
285encode remote call between a client and a server.</p>
286
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]287<h2><a name="tree">The tree output</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]288
289<p>The parser returns a tree built during the document analysis. The value
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]290returned is an <strong>xmlDocPtr</strong> (i.e. a pointer to an
291<strong>xmlDoc</strong> structure). This structure contains informations like
292the file name, the document type, and a <strong>root</strong> pointer which
293is the root of the document (or more exactly the first child under the root
294which is the document). The tree is made of <strong>xmlNode</strong>s, chained
295in double linked lists of siblings and with childs&lt;->parent relationship.
296An xmlNode can also carry properties (a chain of xmlAttr structures). An
297attribute may have a value which is a list of TEXT or ENTITY_REF nodes.</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]298
299<p>Here is an example (erroneous w.r.t. the XML spec since there should be
300only one ELEMENT under the root):</p>
301
302<p><img src="structure.gif" alt=" structure.gif "></p>
303
304<p>In the source package there is a small program (not installed by default)
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]305called <strong>tester</strong> which parses XML files given as argument and
306prints them back as parsed, this is useful to detect errors both in XML code
307and in the XML parser itself. It has an option <strong>--debug</strong> which
308prints the actual in-memory structure of the document, here is the result with
309the <a href="#example">example</a> given before:</p>
310<pre>DOCUMENT
311version=1.0
312standalone=true
313 ELEMENT EXAMPLE
314 ATTRIBUTE prop1
315 TEXT
316 content=gnome is great
317 ATTRIBUTE prop2
318 ENTITY_REF
319 TEXT
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]320 content= linux too
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]321 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]322 TEXT
323 content=Welcome to Gnome
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]324 ELEMENT chapter
325 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]326 TEXT
327 content=The Linux adventure
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]328 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]329 TEXT
330 content=bla bla bla ...
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]331 ELEMENT image
332 ATTRIBUTE href
333 TEXT
334 content=linus.gif
335 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]336 TEXT
337 content=...</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]338
339<p>This should be useful to learn the internal representation model.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]340
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]341<h2><a name="interface">The SAX interface</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]342
343<p>Sometimes the DOM tree output is just to large to fit reasonably into
344memory. In that case and if you don't expect to save back the XML document
345loaded using libxml, it's better to use the SAX interface of libxml. SAX is a
346<strong>callback based interface</strong> to the parser. Before parsing, the
347application layer register a customized set of callbacks which will be called
348by the library as it progresses through the XML input.</p>
349
350<p>To get a more detailed step-by-step guidance on using the SAX interface of
351libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> made <a
352href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice
353documentation.</a></p>
354
355<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
356program located in the gnome-xml module (it's usually not shipped in the
357binary packages of libxml, but you can also find it in the tar source
358distribution). Here is the sequence of callback that would be generated when
359parsing the example given before as reported by testSAX:</p>
360<pre>SAX.setDocumentLocator()
361SAX.startDocument()
362SAX.getEntity(amp)
363SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp;amp; linux too')
364SAX.characters( , 3)
365SAX.startElement(head)
366SAX.characters( , 4)
367SAX.startElement(title)
368SAX.characters(Welcome to Gnome, 16)
369SAX.endElement(title)
370SAX.characters( , 3)
371SAX.endElement(head)
372SAX.characters( , 3)
373SAX.startElement(chapter)
374SAX.characters( , 4)
375SAX.startElement(title)
376SAX.characters(The Linux adventure, 19)
377SAX.endElement(title)
378SAX.characters( , 4)
379SAX.startElement(p)
380SAX.characters(bla bla bla ..., 15)
381SAX.endElement(p)
382SAX.characters( , 4)
383SAX.startElement(image, href='linus.gif')
384SAX.endElement(image)
385SAX.characters( , 4)
386SAX.startElement(p)
387SAX.characters(..., 3)
388SAX.endElement(p)
389SAX.characters( , 3)
390SAX.endElement(chapter)
391SAX.characters( , 1)
392SAX.endElement(EXAMPLE)
393SAX.endDocument()</pre>
394
395<p>Most of the other functionnalities of libxml are based on the DOM tree
396building facility, so nearly everything up to the end of this document
397presuppose the use of the standard DOM tree build. Note that the DOM tree
398itself is built by a set of registered default callbacks, without internal
399specific interface.</p>
400
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]401<h2><a name="library">The XML library interfaces</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]402
403<p>This section is directly intended to help programmers getting bootstrapped
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]404using the XML library from the C language. It doesn't intent to be extensive,
405I hope the automatically generated docs will provide the completeness
406required, but as a separated set of documents. The interfaces of the XML
407library are by principle low level, there is nearly zero abstration. Those
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]408interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]409
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]410<p>The <a href="gnome-xml-parser.html">parser interfaces for XML</a> are
411separated from the <a href="gnome-xml-htmlparser.html">HTML parser ones</a>,
412let's have a look at how it can be called:</p>
413
414<h3><a name="Invoking">Invoking the parser : the pull way</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]415
416<p>Usually, the first thing to do is to read an XML input, the parser accepts
417to parse both memory mapped documents or direct files. The functions are
418defined in "parser.h":</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]419<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]420 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
421 <dd><p>parse a zero terminated string containing the document</p>
422 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]423</dl>
424<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]425 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
426 <dd><p>parse an XML document contained in a file (possibly compressed)</p>
427 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]428</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]429
430<p>This returns a pointer to the document structure (or NULL in case of
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]431failure).</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]432
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]433<h3 id="Invoking1">Invoking the parser: the push way</h3>
434
435<p>In order for the application to keep the control when the document is been
436fetched (common for GUI based programs) the libxml, as of version 1.8.3
437provides a push interface too, here are the interfaces:</p>
438<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
439 void *user_data,
440 const char *chunk,
441 int size,
442 const char *filename);
443int xmlParseChunk (xmlParserCtxtPtr ctxt,
444 const char *chunk,
445 int size,
446 int terminate);</pre>
447
448<p>and here is a simple use example:</p>
449<pre> FILE *f;
450
451 f = fopen(filename, "r");
452 if (f != NULL) {
453 int res, size = 1024;
454 char chars[1024];
455 xmlParserCtxtPtr ctxt;
456
457 res = fread(chars, 1, 4, f);
458 if (res > 0) {
459 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
460 chars, res, filename);
461 while ((res = fread(chars, 1, size, f)) > 0) {
462 xmlParseChunk(ctxt, chars, res, 0);
463 }
464 xmlParseChunk(ctxt, chars, 0, 1);
465 doc = ctxt->myDoc;
466 xmlFreeParserCtxt(ctxt);
467 }
468 }</pre>
469
470<p>Also note that the HTML parser embedded into libxml also have a push
471interface they are just prefixed by "html" instead of "xml"</p>
472
473<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
474
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]475<p>A couple of comments can be made, first this mean that the parser is
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]476memory-hungry, first to load the document in memory, second to build the tree.
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]477Reading a document without building the tree is possible using the SAX
478interfaces (see SAX.h and <a
479href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
480Henstridge documentation</a>), not also that the push interface can be limited
481to SAX, just use the two first arguments of
482<code>xmlCreatePushParserCtxt()</code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]483
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]484<h3><a name="Building">Building a tree from scratch</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]485
486<p>The other way to get an XML tree in memory is by building it. Basically
487there is a set of functions dedicated to building new elements, those are also
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]488described in "tree.h", here is for example the piece of code producing the
489example used before:</p>
490<pre> xmlDocPtr doc;
491 xmlNodePtr tree, subtree;
492
493 doc = xmlNewDoc("1.0");
494 doc->root = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
495 xmlSetProp(doc->root, "prop1", "gnome is great");
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]496 xmlSetProp(doc->root, "prop2", "&amp; linux too");
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]497 tree = xmlNewChild(doc->root, NULL, "head", NULL);
498 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
499 tree = xmlNewChild(doc->root, NULL, "chapter", NULL);
500 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
501 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
502 subtree = xmlNewChild(tree, NULL, "image", NULL);
503 xmlSetProp(subtree, "href", "linus.gif");</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]504
505<p>Not really rocket science ...</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]506
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]507<h3><a name="Traversing">Traversing the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]508
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]509<p>Basically by <a href="gnome-xml-tree.html">including "tree.h"</a> your code
510has access to the internal structure of all the element of the tree. The names
511should be somewhat simple like <strong>parent</strong>,
512<strong>childs</strong>, <strong>next</strong>, <strong>prev</strong>,
513<strong>properties</strong>, etc... For example still with the previous
514example:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]515<pre><code>doc->root->childs->childs</code></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]516
517<p>points to the title element,</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]518<pre>doc->root->childs->next->child->child</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]519
520<p>points to the text node containing the chapter titlle "The Linux adventure"
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]521and</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]522
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]523<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
524present before the document root, so doc->root may point to an element which
525is not the document Root Element, a function
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]526<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]527
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]528<h3><a name="Modifying">Modifying the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]529
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]530<p>functions are provided to read and write the document content, here is an
531excerpt from the <a href="gnome-xml-tree.html">tree API</a>:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]532<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]533 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
534 xmlChar *value);</code></dt>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]535 <dd><p>This set (or change) an attribute carried by an ELEMENT node the
536 value can be NULL</p>
537 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]538</dl>
539<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]540 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]541 *name);</code></dt>
542 <dd><p>This function returns a pointer to the property content, note that
543 no extra copy is made</p>
544 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]545</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]546
547<p>Two functions must be used to read an write the text associated to
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]548elements:</p>
549<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]550 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]551 *value);</code></dt>
552 <dd><p>This function takes an "external" string and convert it to one text
553 node or possibly to a list of entity and text nodes. All non-predefined
554 entity references like &amp;Gnome; will be stored internally as an
555 entity node, hence the result of the function may not be a single
556 node.</p>
557 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]558</dl>
559<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]560 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]561 inLine);</code></dt>
562 <dd><p>this is the dual function, which generate a new string containing
563 the content of the text and entity nodes. Note the extra argument
564 inLine, if set to 1 instead of returning the &amp;Gnome; XML encoding in
565 the string it will substitute it with it's value say "GNU Network Object
566 Model Environment". Set it if you want to use the string for non XML
567 usage like User Interface.</p>
568 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]569</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]570
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]571<h3><a name="Saving">Saving a tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]572
573<p>Basically 3 options are possible:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]574<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]575 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]576 *size);</code></dt>
577 <dd><p>returns a buffer where the document has been saved</p>
578 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]579</dl>
580<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]581 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
582 <dd><p>dumps a buffer to an open file descriptor</p>
583 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]584</dl>
585<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]586 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
587 <dd><p>save the document ot a file. In that case the compression interface
588 is triggered if turned on</p>
589 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]590</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]591
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]592<h3><a name="Compressio">Compression</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]593
594<p>The library handle transparently compression when doing file based
595accesses, the level of compression on saves can be tuned either globally or
596individually for one file:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]597<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]598 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
599 <dd><p>Get the document compression ratio (0-9)</p>
600 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]601</dl>
602<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]603 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
604 <dd><p>Set the document compression ratio</p>
605 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]606</dl>
607<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]608 <dt><code>int xmlGetCompressMode(void);</code></dt>
609 <dd><p>Get the default compression ratio</p>
610 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]611</dl>
612<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]613 <dt><code>void xmlSetCompressMode(int mode);</code></dt>
614 <dd><p>set the default compression ratio</p>
615 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]616</dl>
617
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]618<h2><a name="Entities">Entities or no entities</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]619
620<p>Entities principle is similar to simple C macros. They define an
621abbreviation for a given string that you can reuse many time through the
622content of your document. They are especially useful when frequent occurrences
623of a given string may occur within a document or to confine the change needed
624to a document to a restricted area in the internal subset of the document (at
625the beginning). Example:</p>
626<pre>1 &lt;?xml version="1.0"?>
6272 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
6283 &lt;!ENTITY xml "Extensible Markup Language">
6294 ]>
6305 &lt;EXAMPLE>
6316 &amp;xml;
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]6327 &lt;/EXAMPLE></pre>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]633
634<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]635it's name with '&amp;' and following it by ';' without any spaces added. There
636are 5 predefined entities in libxml allowing to escape charaters with
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]637predefined meaning in some parts of the xml document content:
638<strong>&amp;lt;</strong> for the letter '&lt;', <strong>&amp;gt;</strong> for
639the letter '>', <strong>&amp;apos;</strong> for the letter ''',
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]640<strong>&amp;quot;</strong> for the letter '"', and <strong>&amp;amp;</strong>
641for the letter '&amp;'.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]642
643<p>One of the problems related to entities is that you may want the parser to
644substitute entities content to see the replacement text in your application,
645or you may prefer keeping entities references as such in the content to be
646able to save the document back without loosing this usually precious
647information (if the user went through the pain of explicitley defining
648entities, he may have a a rather negative attitude if you blindly susbtitute
649them as saving time). The function <a
650href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
651allows to check and change the behaviour, which is to not substitute entities
652by default.</p>
653
654<p>Here is the DOM tree built by libxml for the previous document in the
655default case:</p>
656<pre>/gnome/src/gnome-xml -> ./tester --debug test/ent1
657DOCUMENT
658version=1.0
659 ELEMENT EXAMPLE
660 TEXT
661 content=
662 ENTITY_REF
663 INTERNAL_GENERAL_ENTITY xml
664 content=Extensible Markup Language
665 TEXT
666 content=</pre>
667
668<p>And here is the result when substituting entities:</p>
669<pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
670DOCUMENT
671version=1.0
672 ELEMENT EXAMPLE
673 TEXT
674 content= Extensible Markup Language</pre>
675
676<p>So entities or no entities ? Basically it depends on your use case, I
677suggest to keep the non-substituting default behaviour and avoid using
678entities in your XML document or data if you are not willing to handle the
679entity references elements in the DOM tree.</p>
680
681<p>Note that at save time libxml enforce the conversion of the predefined
682entities where necessary to prevent well-formedness problems, and will also
683transparently replace those with chars (i.e. will not generate entity
684reference elements in the DOM tree nor call the reference() SAX callback when
685finding them in the input).</p>
686
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]687<h2><a name="Namespaces">Namespaces</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]688
689<p>The libxml library implement namespace @@ support by recognizing namespace
690contructs in the input, and does namespace lookup automatically when building
691the DOM tree. A namespace declaration is associated with an in-memory
692structure and all elements or attributes within that namespace point to it.
693Hence testing the namespace is a simple and fast equality operation at the
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]694user level.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]695
696<p>I suggest it that people using libxml use a namespace, and declare it on
697the root element of their document as the default namespace. Then they dont
698need to happend the prefix in the content but we will have a basis for future
699semantic refinement and merging of data from different sources. This doesn't
700augment significantly the size of the XML output, but significantly increase
701it's value in the long-term.</p>
702
703<p>Concerning the namespace value, this has to be an URL, but this doesn't
704have to point to any existing resource on the Web. I suggest using an URL
705within a domain you control, which makes sense and if possible holding some
706kind of versionning informations. For example
707<code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme.
708Then when you load a file, make sure that a namespace carrying the
709version-independant prefix is installed on the root element of your document,
710and if the version information don't match something you know, warn the user
711and be liberal in what you accept as the input. Also do *not* try to base
712namespace checking on the prefix value &lt;foo:text> may be exactly the same
713as &lt;bar:text> in another document, what really matter is the URI
714associated with the element or the attribute, not the prefix string which is
715just a shortcut for the full URI.</p>
716
717<p>@@Interfaces@@</p>
718
719<p>@@Examples@@</p>
720
721<p>Usually people object using namespace in the case of validation, I object
722this and will make sure that using namespaces won't break validity checking,
723so even is you plan or are using validation I strongly suggest to add
724namespaces to your document. A default namespace scheme
725<code>xmlns="http://...."</code> should not break validity even on less
726flexible parsers. Now using namespace to mix and differenciate content coming
727from mutliple Dtd will certainly break current validation schemes, I will try
728to provide ways to do this, but this may not be portable or standardized.</p>
729
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]730<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]731
732<p>Well what is validation and what is a DTD ?</p>
733
734<p>Validation is the process of checking a document against a set of
735construction rules, a <strong>DTD</strong> (Document Type Definition) is such
736a set of rules.</p>
737
738<p>The validation process and building DTDs are the two most difficult parts
739of XML life cycle. Briefly a DTD defines all the possibles element to be
740found within your document, what is the formal shape of your document tree (by
741defining the allowed content of an element, either text, a regular expression
742for the allowed list of children, or mixed content i.e. both text and childs).
743The DTD also defines the allowed attributes for all elements and the types of
744the attributes. For more detailed informations, I suggest to read the related
745parts of the XML specification, the examples found under
746gnome-xml/test/valid/dtd and the large amount of books available on XML. The
747dia example in gnome-xml/test/valid should be both simple and complete enough
748to allow you to build your own.</p>
749
750<p>A word of warning, building a good DTD which will fit your needs of your
751application in the long-term is far from trivial, however the extra level of
752quality it can insure is well worth the price for some sets of applications or
753if you already have already a DTD defined for your application field.</p>
754
755<p>The validation is not completely finished but in a (very IMHO) usable
756state. Until a real validation interface is defined the way to do it is to
757define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external
758variable to 1, this will of course be changed at some point:</p>
759
760<p>extern int xmlDoValidityCheckingDefaultValue;</p>
761
762<p>...</p>
763
764<p>xmlDoValidityCheckingDefaultValue = 1;</p>
765
766<p></p>
767
768<p>To handle external entities, use the function
769<strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to
770link in you HTTP/FTP/Entities database library to the standard libxml
771core.</p>
772
773<p>@@interfaces@@</p>
774
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]775<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]776
777<p><a href="http://www.w3.org/DOM/">DOM</a> stands for the <em>Document Object
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]778Model</em> this is an API for accessing XML or HTML structured documents.
779Native support for DOM in Gnome is on the way (module gnome-dom), and it will
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]780be based on gnome-xml. This will be a far cleaner interface to manipulate XML
Daniel Veillardc08a2c61999-09-08 21:35:25 +0000[diff] [blame]781files within Gnome since it won't expose the internal structure. DOM defines a
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]782set of IDL (or Java) interfaces allowing to traverse and manipulate a
783document. The DOM library will allow accessing and modifying "live" documents
784presents on other programs like this:</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]785
786<p><img src="DOM.gif" alt=" DOM.gif "></p>
787
788<p>This should help greatly doing things like modifying a gnumeric spreadsheet
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]789embedded in a GWP document for example.</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]790
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]791<p>The current DOM implementation on top of libxml is the <a
792href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module</a>, this is
793a full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph
794Levien</a>.</p>
795
796<p>The gnome-dom module in the Gnome CVS base is obsolete</p>
797
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]798<h2><a name="Example"></a><a name="real">A real example</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]799
800<p>Here is a real size example, where the actual content of the application
801data is not kept in the DOM tree but uses internal structures. It is based on
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]802a proposal to keep a database of jobs related to Gnome, with an XML based
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]803storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
804base</a>:</p>
805<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]806&lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
807 &lt;gjob:Jobs>
808
809 &lt;gjob:Job>
810 &lt;gjob:Project ID="3"/>
811 &lt;gjob:Application>GBackup&lt;/gjob:Application>
812 &lt;gjob:Category>Development&lt;/gjob:Category>
813
814 &lt;gjob:Update>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]815 &lt;gjob:Status>Open&lt;/gjob:Status>
816 &lt;gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST&lt;/gjob:Modified>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]817 &lt;gjob:Salary>USD 0.00&lt;/gjob:Salary>
818 &lt;/gjob:Update>
819
820 &lt;gjob:Developers>
821 &lt;gjob:Developer>
822 &lt;/gjob:Developer>
823 &lt;/gjob:Developers>
824
825 &lt;gjob:Contact>
826 &lt;gjob:Person>Nathan Clemons&lt;/gjob:Person>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]827 &lt;gjob:Email>nathan@windsofstorm.net&lt;/gjob:Email>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]828 &lt;gjob:Company>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]829 &lt;/gjob:Company>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]830 &lt;gjob:Organisation>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]831 &lt;/gjob:Organisation>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]832 &lt;gjob:Webpage>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]833 &lt;/gjob:Webpage>
834 &lt;gjob:Snailmail>
835 &lt;/gjob:Snailmail>
836 &lt;gjob:Phone>
837 &lt;/gjob:Phone>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]838 &lt;/gjob:Contact>
839
840 &lt;gjob:Requirements>
841 The program should be released as free software, under the GPL.
842 &lt;/gjob:Requirements>
843
844 &lt;gjob:Skills>
845 &lt;/gjob:Skills>
846
847 &lt;gjob:Details>
848 A GNOME based system that will allow a superuser to configure
849 compressed and uncompressed files and/or file systems to be backed
850 up with a supported media in the system. This should be able to
851 perform via find commands generating a list of files that are passed
852 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
853 or via operations performed on the filesystem itself. Email
854 notification and GUI status display very important.
855 &lt;/gjob:Details>
856
857 &lt;/gjob:Job>
858
859 &lt;/gjob:Jobs>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]860&lt;/gjob:Helping></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]861
862<p>While loading the XML file into an internal DOM tree is a matter of calling
863only a couple of functions, browsing the tree to gather the informations and
864generate the internals structures is harder, and more error prone.</p>
865
866<p>The suggested principle is to be tolerant with respect to the input
867structure. For example the ordering of the attributes is not significant, Cthe
868XML specification is clear about it. It's also usually a good idea to not be
869dependant of the orders of the childs of a given node, unless it really makes
870things harder. Here is some code to parse the informations for a person:</p>
871<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]872 * A person record
873 */
874typedef struct person {
875 char *name;
876 char *email;
877 char *company;
878 char *organisation;
879 char *smail;
880 char *webPage;
881 char *phone;
882} person, *personPtr;
883
884/*
885 * And the code needed to parse it
886 */
887personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
888 personPtr ret = NULL;
889
890DEBUG("parsePerson\n");
891 /*
892 * allocate the struct
893 */
894 ret = (personPtr) malloc(sizeof(person));
895 if (ret == NULL) {
896 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]897 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]898 }
899 memset(ret, 0, sizeof(person));
900
901 /* We don't care what the top level element name is */
902 cur = cur->childs;
903 while (cur != NULL) {
904 if ((!strcmp(cur->name, "Person")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]905 ret->name = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]906 if ((!strcmp(cur->name, "Email")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]907 ret->email = xmlNodeListGetString(doc, cur->childs, 1);
908 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]909 }
910
911 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]912}</pre>
913
914<p>Here is a couple of things to notice:</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]915<ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]916 <li>Usually a recursive parsing style is the more convenient one, XML data
917 being by nature subject to repetitive constructs and usualy exibit highly
918 stuctured patterns.</li>
919 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e.
920 the pointer to the global XML document and the namespace reserved to the
921 application. Document wide information are needed for example to decode
922 entities and it's a good coding practice to define a namespace for your
923 application set of data and test that the element and attributes you're
924 analyzing actually pertains to your application space. This is done by a
925 simple equality test (cur->ns == ns).</li>
926 <li>To retrieve text and attributes value, it is suggested to use the
927 function <em>xmlNodeListGetString</em> to gather all the text and entity
928 reference nodes generated by the DOM output and produce an single text
929 string.</li>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]930</ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]931
932<p>Here is another piece of code used to parse another level of the
933structure:</p>
934<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]935 * a Description for a Job
936 */
937typedef struct job {
938 char *projectID;
939 char *application;
940 char *category;
941 personPtr contact;
942 int nbDevelopers;
943 personPtr developers[100]; /* using dynamic alloc is left as an exercise */
944} job, *jobPtr;
945
946/*
947 * And the code needed to parse it
948 */
949jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
950 jobPtr ret = NULL;
951
952DEBUG("parseJob\n");
953 /*
954 * allocate the struct
955 */
956 ret = (jobPtr) malloc(sizeof(job));
957 if (ret == NULL) {
958 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]959 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]960 }
961 memset(ret, 0, sizeof(job));
962
963 /* We don't care what the top level element name is */
964 cur = cur->childs;
965 while (cur != NULL) {
966
967 if ((!strcmp(cur->name, "Project")) &amp;&amp; (cur->ns == ns)) {
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]968 ret->projectID = xmlGetProp(cur, "ID");
969 if (ret->projectID == NULL) {
970 fprintf(stderr, "Project has no ID\n");
971 }
972 }
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]973 if ((!strcmp(cur->name, "Application")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]974 ret->application = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]975 if ((!strcmp(cur->name, "Category")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]976 ret->category = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]977 if ((!strcmp(cur->name, "Contact")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]978 ret->contact = parsePerson(doc, ns, cur);
979 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]980 }
981
982 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]983}</pre>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]984
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]985<p>One can notice that once used to it, writing this kind of code is quite
986simple, but boring. Ultimately, it could be possble to write stubbers taking
987either C data structure definitions, a set of XML examples or an XML DTD and
988produce the code needed to import and export the content between C data and
989XML storage. This is left as an exercise to the reader :-)</p>
990
991<p>Feel free to use <a href="gjobread.c">the code for the full C parsing
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]992example</a> as a template, it is also available with Makefile in the Gnome CVS
993base under gnome-xml/example</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]994
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]995<p></p>
996
997<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>
998
Daniel Veillard461a66c2000-01-18 18:01:01 +0000[diff] [blame^]999<p>$Id: xml.html,v 1.21 2000/01/14 14:45:21 veillard Exp $</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]1000</body>
1001</html>