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blob: 105b19755484e97ed9be4ff8d5b7128c9dbcf681 [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 Veillardda07c342000-01-25 18:31:22 +0000[diff] [blame^]149 <li>there is some kind of roadmap to libxml-2.0: fix I18N, and <a
150 href="http://rpmfind.net/tools/gdome/messages/0039.html">change structures
151 to accomodate DOM</a></li>
152 <li>added a nanoFTP transport module</li>
153</ul>
154
155<h3>1.8.5: Jan 21 2000</h3>
156<ul>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]157 <li>adding APIs to parse a well balanced chunk of XML (production <a
158 href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the XML
159 spec)</li>
Daniel Veillard461a66c2000-01-18 18:01:01 +0000[diff] [blame]160 <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li>
161 <li>Jody Goldberg &lt;jgoldberg@home.com> provided another patch trying to
162 solve the zlib checks problems</li>
163 <li>The current state in gnome CVS base is expected to ship as 1.8.5 with
164 gnumeric soon</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]165</ul>
166
167<h3>1.8.4: Jan 13 2000</h3>
168<ul>
169 <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li>
170 <li>all exit() call should have been removed from libxml</li>
171 <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li>
172 <li>added newDocFragment()</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]173</ul>
174
175<h3>1.8.3: Jan 5 2000</h3>
176<ul>
177 <li>a Push interface for the XML and HTML parsers</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]178 <li>an shell like interface to the document tree (try tester --shell
179 :-)</li>
Daniel Veillarddbfd6411999-12-28 16:35:14 +0000[diff] [blame]180 <li>lots of bug fixes and improvement added over XMas hollidays</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]181 <li>fixed the DTD parsing code to work with the xhtml DTD</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]182 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li>
183 <li>Fixed bugs in xmlNewNs()</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]184 <li>External entity loading code has been revamped, now it uses
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]185 xmlLoadExternalEntity(), some fix on entities processing were added</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]186 <li>cleaned up WIN32 includes of socket stuff</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]187</ul>
188
189<h3>1.8.2: Dec 21 1999</h3>
190<ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]191 <li>I got another problem with includes and C++, I hope this issue is fixed
192 for good this time</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]193 <li>Added a few tree modification functions: xmlReplaceNode,
194 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and
195 xmlDocSetRootElement</li>
196 <li>Tried to improve the HTML output with help from <a
197 href="mailto:clahey@umich.edu">Chris Lahey</a></li>
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]198</ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]199
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]200<h3>1.8.1: Dec 18 1999</h3>
201<ul>
202 <li>various patches to avoid troubles when using libxml with C++ compilers
203 the "namespace" keyword and C escaping in include files</li>
204 <li>a problem in one of the core macros IS_CHAR was corrected</li>
205 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing,
206 and more specifically the Dia application</li>
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]207 <li>fixed a posteriori validation (validation after parsing, or by using a
208 Dtd not specified in the original document)</li>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]209 <li>fixed a bug in</li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]210</ul>
211
212<h3>1.8.0: Dec 12 1999</h3>
213<ul>
214 <li>cleanup, especially memory wise</li>
215 <li>the parser should be more reliable, especially the HTML one, it should
216 not crash, whatever the input !</li>
217 <li>Integrated various patches, especially a speedup improvement for large
218 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>,
219 configure with --with-buffers to enable them.</li>
220 <li>attribute normalization, oops should have been added long ago !</li>
221 <li>attributes defaulted from Dtds should be available, xmlSetProp() now
222 does entities escapting by default.</li>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]223</ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]224
225<h3>1.7.4: Oct 25 1999</h3>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]226<ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]227 <li>Lots of HTML improvement</li>
228 <li>Fixed some errors when saving both XML and HTML</li>
229 <li>More examples, the regression tests should now look clean</li>
230 <li>Fixed a bug with contiguous charref</li>
231</ul>
232
233<h3>1.7.3: Sep 29 1999</h3>
234<ul>
235 <li>portability problems fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]236 <li>snprintf was used unconditionnally, leading to link problems on system
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]237 were it's not available, fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]238</ul>
239
240<h3>1.7.1: Sep 24 1999</h3>
241<ul>
242 <li>The basic type for strings manipulated by libxml has been renamed in
243 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason
244 is that CHAR was conflicting with a predefined type on Windows. However on
245 non WIN32 environment, compatibility is provided by the way of a
246 <strong>#define </strong>.</li>
247 <li>Changed another error : the use of a structure field called errno, and
248 leading to troubles on platforms where it's a macro</li>
249</ul>
250
251<h3>1.7.0: sep 23 1999</h3>
252<ul>
253 <li>Added the ability to fetch remote DTD or parsed entities, see the <a
254 href="gnome-xml-nanohttp.html">nanohttp</a> module.</li>
255 <li>Added an errno to report errors by another mean than a simple printf
256 like callback</li>
257 <li>Finished ID/IDREF support and checking when validation</li>
258 <li>Serious memory leaks fixed (there is now a <a
259 href="gnome-xml-xmlmemory.html">memory wrapper</a> module)</li>
260 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a>
261 implementation</li>
262 <li>Added an HTML parser front-end</li>
263</ul>
264
265<h2><a name="XML">XML</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]266
267<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for markup
268based structured documents, here is <a name="example">an example</a>:</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]269<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]270&lt;EXAMPLE prop1="gnome is great" prop2="&amp;amp; linux too">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]271 &lt;head>
272 &lt;title>Welcome to Gnome&lt;/title>
273 &lt;/head>
274 &lt;chapter>
275 &lt;title>The Linux adventure&lt;/title>
276 &lt;p>bla bla bla ...&lt;/p>
277 &lt;image href="linus.gif"/>
278 &lt;p>...&lt;/p>
279 &lt;/chapter>
280&lt;/EXAMPLE></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]281
282<p>The first line specify that it's an XML document and gives useful
283informations about it's encoding. Then the document is a text format whose
284structure is specified by tags between brackets. <strong>Each tag opened have
285to be closed</strong> XML is pedantic about this, not that for example the
286image tag has no content (just an attribute) and is closed by ending up the
287tag with <code>/></code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]288
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]289<p>XML can be applied sucessfully to a wide range or usage from long term
290structured document maintenance where it follows the steps of SGML to simple
291data encoding mechanism like configuration file format (glade), spreadsheets
292(gnumeric), or even shorter lived document like in WebDAV where it is used to
293encode remote call between a client and a server.</p>
294
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]295<h2><a name="tree">The tree output</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]296
297<p>The parser returns a tree built during the document analysis. The value
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]298returned is an <strong>xmlDocPtr</strong> (i.e. a pointer to an
299<strong>xmlDoc</strong> structure). This structure contains informations like
300the file name, the document type, and a <strong>root</strong> pointer which
301is the root of the document (or more exactly the first child under the root
302which is the document). The tree is made of <strong>xmlNode</strong>s, chained
303in double linked lists of siblings and with childs&lt;->parent relationship.
304An xmlNode can also carry properties (a chain of xmlAttr structures). An
305attribute 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]306
307<p>Here is an example (erroneous w.r.t. the XML spec since there should be
308only one ELEMENT under the root):</p>
309
310<p><img src="structure.gif" alt=" structure.gif "></p>
311
312<p>In the source package there is a small program (not installed by default)
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]313called <strong>tester</strong> which parses XML files given as argument and
314prints them back as parsed, this is useful to detect errors both in XML code
315and in the XML parser itself. It has an option <strong>--debug</strong> which
316prints the actual in-memory structure of the document, here is the result with
317the <a href="#example">example</a> given before:</p>
318<pre>DOCUMENT
319version=1.0
320standalone=true
321 ELEMENT EXAMPLE
322 ATTRIBUTE prop1
323 TEXT
324 content=gnome is great
325 ATTRIBUTE prop2
326 ENTITY_REF
327 TEXT
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]328 content= linux too
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]329 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]330 TEXT
331 content=Welcome to Gnome
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]332 ELEMENT chapter
333 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]334 TEXT
335 content=The Linux adventure
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]336 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]337 TEXT
338 content=bla bla bla ...
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]339 ELEMENT image
340 ATTRIBUTE href
341 TEXT
342 content=linus.gif
343 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]344 TEXT
345 content=...</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]346
347<p>This should be useful to learn the internal representation model.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]348
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]349<h2><a name="interface">The SAX interface</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]350
351<p>Sometimes the DOM tree output is just to large to fit reasonably into
352memory. In that case and if you don't expect to save back the XML document
353loaded using libxml, it's better to use the SAX interface of libxml. SAX is a
354<strong>callback based interface</strong> to the parser. Before parsing, the
355application layer register a customized set of callbacks which will be called
356by the library as it progresses through the XML input.</p>
357
358<p>To get a more detailed step-by-step guidance on using the SAX interface of
359libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> made <a
360href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice
361documentation.</a></p>
362
363<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
364program located in the gnome-xml module (it's usually not shipped in the
365binary packages of libxml, but you can also find it in the tar source
366distribution). Here is the sequence of callback that would be generated when
367parsing the example given before as reported by testSAX:</p>
368<pre>SAX.setDocumentLocator()
369SAX.startDocument()
370SAX.getEntity(amp)
371SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp;amp; linux too')
372SAX.characters( , 3)
373SAX.startElement(head)
374SAX.characters( , 4)
375SAX.startElement(title)
376SAX.characters(Welcome to Gnome, 16)
377SAX.endElement(title)
378SAX.characters( , 3)
379SAX.endElement(head)
380SAX.characters( , 3)
381SAX.startElement(chapter)
382SAX.characters( , 4)
383SAX.startElement(title)
384SAX.characters(The Linux adventure, 19)
385SAX.endElement(title)
386SAX.characters( , 4)
387SAX.startElement(p)
388SAX.characters(bla bla bla ..., 15)
389SAX.endElement(p)
390SAX.characters( , 4)
391SAX.startElement(image, href='linus.gif')
392SAX.endElement(image)
393SAX.characters( , 4)
394SAX.startElement(p)
395SAX.characters(..., 3)
396SAX.endElement(p)
397SAX.characters( , 3)
398SAX.endElement(chapter)
399SAX.characters( , 1)
400SAX.endElement(EXAMPLE)
401SAX.endDocument()</pre>
402
403<p>Most of the other functionnalities of libxml are based on the DOM tree
404building facility, so nearly everything up to the end of this document
405presuppose the use of the standard DOM tree build. Note that the DOM tree
406itself is built by a set of registered default callbacks, without internal
407specific interface.</p>
408
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]409<h2><a name="library">The XML library interfaces</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]410
411<p>This section is directly intended to help programmers getting bootstrapped
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]412using the XML library from the C language. It doesn't intent to be extensive,
413I hope the automatically generated docs will provide the completeness
414required, but as a separated set of documents. The interfaces of the XML
415library are by principle low level, there is nearly zero abstration. Those
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]416interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]417
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]418<p>The <a href="gnome-xml-parser.html">parser interfaces for XML</a> are
419separated from the <a href="gnome-xml-htmlparser.html">HTML parser ones</a>,
420let's have a look at how it can be called:</p>
421
422<h3><a name="Invoking">Invoking the parser : the pull way</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]423
424<p>Usually, the first thing to do is to read an XML input, the parser accepts
425to parse both memory mapped documents or direct files. The functions are
426defined in "parser.h":</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]427<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]428 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
429 <dd><p>parse a zero terminated string containing the document</p>
430 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]431</dl>
432<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]433 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
434 <dd><p>parse an XML document contained in a file (possibly compressed)</p>
435 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]436</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]437
438<p>This returns a pointer to the document structure (or NULL in case of
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]439failure).</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]440
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]441<h3 id="Invoking1">Invoking the parser: the push way</h3>
442
443<p>In order for the application to keep the control when the document is been
444fetched (common for GUI based programs) the libxml, as of version 1.8.3
445provides a push interface too, here are the interfaces:</p>
446<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
447 void *user_data,
448 const char *chunk,
449 int size,
450 const char *filename);
451int xmlParseChunk (xmlParserCtxtPtr ctxt,
452 const char *chunk,
453 int size,
454 int terminate);</pre>
455
456<p>and here is a simple use example:</p>
457<pre> FILE *f;
458
459 f = fopen(filename, "r");
460 if (f != NULL) {
461 int res, size = 1024;
462 char chars[1024];
463 xmlParserCtxtPtr ctxt;
464
465 res = fread(chars, 1, 4, f);
466 if (res > 0) {
467 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
468 chars, res, filename);
469 while ((res = fread(chars, 1, size, f)) > 0) {
470 xmlParseChunk(ctxt, chars, res, 0);
471 }
472 xmlParseChunk(ctxt, chars, 0, 1);
473 doc = ctxt->myDoc;
474 xmlFreeParserCtxt(ctxt);
475 }
476 }</pre>
477
478<p>Also note that the HTML parser embedded into libxml also have a push
479interface they are just prefixed by "html" instead of "xml"</p>
480
481<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
482
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]483<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]484memory-hungry, first to load the document in memory, second to build the tree.
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]485Reading a document without building the tree is possible using the SAX
486interfaces (see SAX.h and <a
487href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
488Henstridge documentation</a>), not also that the push interface can be limited
489to SAX, just use the two first arguments of
490<code>xmlCreatePushParserCtxt()</code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]491
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]492<h3><a name="Building">Building a tree from scratch</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]493
494<p>The other way to get an XML tree in memory is by building it. Basically
495there is a set of functions dedicated to building new elements, those are also
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]496described in "tree.h", here is for example the piece of code producing the
497example used before:</p>
498<pre> xmlDocPtr doc;
499 xmlNodePtr tree, subtree;
500
501 doc = xmlNewDoc("1.0");
502 doc->root = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
503 xmlSetProp(doc->root, "prop1", "gnome is great");
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]504 xmlSetProp(doc->root, "prop2", "&amp; linux too");
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]505 tree = xmlNewChild(doc->root, NULL, "head", NULL);
506 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
507 tree = xmlNewChild(doc->root, NULL, "chapter", NULL);
508 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
509 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
510 subtree = xmlNewChild(tree, NULL, "image", NULL);
511 xmlSetProp(subtree, "href", "linus.gif");</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]512
513<p>Not really rocket science ...</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]514
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]515<h3><a name="Traversing">Traversing the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]516
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]517<p>Basically by <a href="gnome-xml-tree.html">including "tree.h"</a> your code
518has access to the internal structure of all the element of the tree. The names
519should be somewhat simple like <strong>parent</strong>,
520<strong>childs</strong>, <strong>next</strong>, <strong>prev</strong>,
521<strong>properties</strong>, etc... For example still with the previous
522example:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]523<pre><code>doc->root->childs->childs</code></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]524
525<p>points to the title element,</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]526<pre>doc->root->childs->next->child->child</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]527
528<p>points to the text node containing the chapter titlle "The Linux adventure"
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]529and</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]530
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]531<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
532present before the document root, so doc->root may point to an element which
533is not the document Root Element, a function
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]534<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]535
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]536<h3><a name="Modifying">Modifying the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]537
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]538<p>functions are provided to read and write the document content, here is an
539excerpt from the <a href="gnome-xml-tree.html">tree API</a>:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]540<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]541 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
542 xmlChar *value);</code></dt>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]543 <dd><p>This set (or change) an attribute carried by an ELEMENT node the
544 value can be NULL</p>
545 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]546</dl>
547<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]548 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]549 *name);</code></dt>
550 <dd><p>This function returns a pointer to the property content, note that
551 no extra copy is made</p>
552 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]553</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]554
555<p>Two functions must be used to read an write the text associated to
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]556elements:</p>
557<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]558 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]559 *value);</code></dt>
560 <dd><p>This function takes an "external" string and convert it to one text
561 node or possibly to a list of entity and text nodes. All non-predefined
562 entity references like &amp;Gnome; will be stored internally as an
563 entity node, hence the result of the function may not be a single
564 node.</p>
565 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]566</dl>
567<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]568 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]569 inLine);</code></dt>
570 <dd><p>this is the dual function, which generate a new string containing
571 the content of the text and entity nodes. Note the extra argument
572 inLine, if set to 1 instead of returning the &amp;Gnome; XML encoding in
573 the string it will substitute it with it's value say "GNU Network Object
574 Model Environment". Set it if you want to use the string for non XML
575 usage like User Interface.</p>
576 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]577</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]578
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]579<h3><a name="Saving">Saving a tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]580
581<p>Basically 3 options are possible:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]582<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]583 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]584 *size);</code></dt>
585 <dd><p>returns a buffer where the document has been saved</p>
586 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]587</dl>
588<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]589 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
590 <dd><p>dumps a buffer to an open file descriptor</p>
591 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]592</dl>
593<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]594 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
595 <dd><p>save the document ot a file. In that case the compression interface
596 is triggered if turned on</p>
597 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]598</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]599
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]600<h3><a name="Compressio">Compression</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]601
602<p>The library handle transparently compression when doing file based
603accesses, the level of compression on saves can be tuned either globally or
604individually for one file:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]605<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]606 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
607 <dd><p>Get the document compression ratio (0-9)</p>
608 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]609</dl>
610<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]611 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
612 <dd><p>Set the document compression ratio</p>
613 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]614</dl>
615<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]616 <dt><code>int xmlGetCompressMode(void);</code></dt>
617 <dd><p>Get the default compression ratio</p>
618 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]619</dl>
620<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]621 <dt><code>void xmlSetCompressMode(int mode);</code></dt>
622 <dd><p>set the default compression ratio</p>
623 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]624</dl>
625
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]626<h2><a name="Entities">Entities or no entities</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]627
628<p>Entities principle is similar to simple C macros. They define an
629abbreviation for a given string that you can reuse many time through the
630content of your document. They are especially useful when frequent occurrences
631of a given string may occur within a document or to confine the change needed
632to a document to a restricted area in the internal subset of the document (at
633the beginning). Example:</p>
634<pre>1 &lt;?xml version="1.0"?>
6352 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
6363 &lt;!ENTITY xml "Extensible Markup Language">
6374 ]>
6385 &lt;EXAMPLE>
6396 &amp;xml;
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]6407 &lt;/EXAMPLE></pre>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]641
642<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]643it's name with '&amp;' and following it by ';' without any spaces added. There
644are 5 predefined entities in libxml allowing to escape charaters with
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]645predefined meaning in some parts of the xml document content:
646<strong>&amp;lt;</strong> for the letter '&lt;', <strong>&amp;gt;</strong> for
647the letter '>', <strong>&amp;apos;</strong> for the letter ''',
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]648<strong>&amp;quot;</strong> for the letter '"', and <strong>&amp;amp;</strong>
649for the letter '&amp;'.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]650
651<p>One of the problems related to entities is that you may want the parser to
652substitute entities content to see the replacement text in your application,
653or you may prefer keeping entities references as such in the content to be
654able to save the document back without loosing this usually precious
655information (if the user went through the pain of explicitley defining
656entities, he may have a a rather negative attitude if you blindly susbtitute
657them as saving time). The function <a
658href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
659allows to check and change the behaviour, which is to not substitute entities
660by default.</p>
661
662<p>Here is the DOM tree built by libxml for the previous document in the
663default case:</p>
664<pre>/gnome/src/gnome-xml -> ./tester --debug test/ent1
665DOCUMENT
666version=1.0
667 ELEMENT EXAMPLE
668 TEXT
669 content=
670 ENTITY_REF
671 INTERNAL_GENERAL_ENTITY xml
672 content=Extensible Markup Language
673 TEXT
674 content=</pre>
675
676<p>And here is the result when substituting entities:</p>
677<pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
678DOCUMENT
679version=1.0
680 ELEMENT EXAMPLE
681 TEXT
682 content= Extensible Markup Language</pre>
683
684<p>So entities or no entities ? Basically it depends on your use case, I
685suggest to keep the non-substituting default behaviour and avoid using
686entities in your XML document or data if you are not willing to handle the
687entity references elements in the DOM tree.</p>
688
689<p>Note that at save time libxml enforce the conversion of the predefined
690entities where necessary to prevent well-formedness problems, and will also
691transparently replace those with chars (i.e. will not generate entity
692reference elements in the DOM tree nor call the reference() SAX callback when
693finding them in the input).</p>
694
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]695<h2><a name="Namespaces">Namespaces</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]696
697<p>The libxml library implement namespace @@ support by recognizing namespace
698contructs in the input, and does namespace lookup automatically when building
699the DOM tree. A namespace declaration is associated with an in-memory
700structure and all elements or attributes within that namespace point to it.
701Hence testing the namespace is a simple and fast equality operation at the
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]702user level.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]703
704<p>I suggest it that people using libxml use a namespace, and declare it on
705the root element of their document as the default namespace. Then they dont
706need to happend the prefix in the content but we will have a basis for future
707semantic refinement and merging of data from different sources. This doesn't
708augment significantly the size of the XML output, but significantly increase
709it's value in the long-term.</p>
710
711<p>Concerning the namespace value, this has to be an URL, but this doesn't
712have to point to any existing resource on the Web. I suggest using an URL
713within a domain you control, which makes sense and if possible holding some
714kind of versionning informations. For example
715<code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme.
716Then when you load a file, make sure that a namespace carrying the
717version-independant prefix is installed on the root element of your document,
718and if the version information don't match something you know, warn the user
719and be liberal in what you accept as the input. Also do *not* try to base
720namespace checking on the prefix value &lt;foo:text> may be exactly the same
721as &lt;bar:text> in another document, what really matter is the URI
722associated with the element or the attribute, not the prefix string which is
723just a shortcut for the full URI.</p>
724
725<p>@@Interfaces@@</p>
726
727<p>@@Examples@@</p>
728
729<p>Usually people object using namespace in the case of validation, I object
730this and will make sure that using namespaces won't break validity checking,
731so even is you plan or are using validation I strongly suggest to add
732namespaces to your document. A default namespace scheme
733<code>xmlns="http://...."</code> should not break validity even on less
734flexible parsers. Now using namespace to mix and differenciate content coming
735from mutliple Dtd will certainly break current validation schemes, I will try
736to provide ways to do this, but this may not be portable or standardized.</p>
737
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]738<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]739
740<p>Well what is validation and what is a DTD ?</p>
741
742<p>Validation is the process of checking a document against a set of
743construction rules, a <strong>DTD</strong> (Document Type Definition) is such
744a set of rules.</p>
745
746<p>The validation process and building DTDs are the two most difficult parts
747of XML life cycle. Briefly a DTD defines all the possibles element to be
748found within your document, what is the formal shape of your document tree (by
749defining the allowed content of an element, either text, a regular expression
750for the allowed list of children, or mixed content i.e. both text and childs).
751The DTD also defines the allowed attributes for all elements and the types of
752the attributes. For more detailed informations, I suggest to read the related
753parts of the XML specification, the examples found under
754gnome-xml/test/valid/dtd and the large amount of books available on XML. The
755dia example in gnome-xml/test/valid should be both simple and complete enough
756to allow you to build your own.</p>
757
758<p>A word of warning, building a good DTD which will fit your needs of your
759application in the long-term is far from trivial, however the extra level of
760quality it can insure is well worth the price for some sets of applications or
761if you already have already a DTD defined for your application field.</p>
762
763<p>The validation is not completely finished but in a (very IMHO) usable
764state. Until a real validation interface is defined the way to do it is to
765define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external
766variable to 1, this will of course be changed at some point:</p>
767
768<p>extern int xmlDoValidityCheckingDefaultValue;</p>
769
770<p>...</p>
771
772<p>xmlDoValidityCheckingDefaultValue = 1;</p>
773
774<p></p>
775
776<p>To handle external entities, use the function
777<strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to
778link in you HTTP/FTP/Entities database library to the standard libxml
779core.</p>
780
781<p>@@interfaces@@</p>
782
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]783<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]784
785<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]786Model</em> this is an API for accessing XML or HTML structured documents.
787Native 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]788be based on gnome-xml. This will be a far cleaner interface to manipulate XML
Daniel Veillardc08a2c61999-09-08 21:35:25 +0000[diff] [blame]789files within Gnome since it won't expose the internal structure. DOM defines a
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]790set of IDL (or Java) interfaces allowing to traverse and manipulate a
791document. The DOM library will allow accessing and modifying "live" documents
792presents on other programs like this:</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]793
794<p><img src="DOM.gif" alt=" DOM.gif "></p>
795
796<p>This should help greatly doing things like modifying a gnumeric spreadsheet
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]797embedded in a GWP document for example.</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]798
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]799<p>The current DOM implementation on top of libxml is the <a
800href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module</a>, this is
801a full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph
802Levien</a>.</p>
803
804<p>The gnome-dom module in the Gnome CVS base is obsolete</p>
805
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]806<h2><a name="Example"></a><a name="real">A real example</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]807
808<p>Here is a real size example, where the actual content of the application
809data 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]810a proposal to keep a database of jobs related to Gnome, with an XML based
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]811storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
812base</a>:</p>
813<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]814&lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
815 &lt;gjob:Jobs>
816
817 &lt;gjob:Job>
818 &lt;gjob:Project ID="3"/>
819 &lt;gjob:Application>GBackup&lt;/gjob:Application>
820 &lt;gjob:Category>Development&lt;/gjob:Category>
821
822 &lt;gjob:Update>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]823 &lt;gjob:Status>Open&lt;/gjob:Status>
824 &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]825 &lt;gjob:Salary>USD 0.00&lt;/gjob:Salary>
826 &lt;/gjob:Update>
827
828 &lt;gjob:Developers>
829 &lt;gjob:Developer>
830 &lt;/gjob:Developer>
831 &lt;/gjob:Developers>
832
833 &lt;gjob:Contact>
834 &lt;gjob:Person>Nathan Clemons&lt;/gjob:Person>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]835 &lt;gjob:Email>nathan@windsofstorm.net&lt;/gjob:Email>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]836 &lt;gjob:Company>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]837 &lt;/gjob:Company>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]838 &lt;gjob:Organisation>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]839 &lt;/gjob:Organisation>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]840 &lt;gjob:Webpage>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]841 &lt;/gjob:Webpage>
842 &lt;gjob:Snailmail>
843 &lt;/gjob:Snailmail>
844 &lt;gjob:Phone>
845 &lt;/gjob:Phone>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]846 &lt;/gjob:Contact>
847
848 &lt;gjob:Requirements>
849 The program should be released as free software, under the GPL.
850 &lt;/gjob:Requirements>
851
852 &lt;gjob:Skills>
853 &lt;/gjob:Skills>
854
855 &lt;gjob:Details>
856 A GNOME based system that will allow a superuser to configure
857 compressed and uncompressed files and/or file systems to be backed
858 up with a supported media in the system. This should be able to
859 perform via find commands generating a list of files that are passed
860 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
861 or via operations performed on the filesystem itself. Email
862 notification and GUI status display very important.
863 &lt;/gjob:Details>
864
865 &lt;/gjob:Job>
866
867 &lt;/gjob:Jobs>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]868&lt;/gjob:Helping></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]869
870<p>While loading the XML file into an internal DOM tree is a matter of calling
871only a couple of functions, browsing the tree to gather the informations and
872generate the internals structures is harder, and more error prone.</p>
873
874<p>The suggested principle is to be tolerant with respect to the input
875structure. For example the ordering of the attributes is not significant, Cthe
876XML specification is clear about it. It's also usually a good idea to not be
877dependant of the orders of the childs of a given node, unless it really makes
878things harder. Here is some code to parse the informations for a person:</p>
879<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]880 * A person record
881 */
882typedef struct person {
883 char *name;
884 char *email;
885 char *company;
886 char *organisation;
887 char *smail;
888 char *webPage;
889 char *phone;
890} person, *personPtr;
891
892/*
893 * And the code needed to parse it
894 */
895personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
896 personPtr ret = NULL;
897
898DEBUG("parsePerson\n");
899 /*
900 * allocate the struct
901 */
902 ret = (personPtr) malloc(sizeof(person));
903 if (ret == NULL) {
904 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]905 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]906 }
907 memset(ret, 0, sizeof(person));
908
909 /* We don't care what the top level element name is */
910 cur = cur->childs;
911 while (cur != NULL) {
912 if ((!strcmp(cur->name, "Person")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]913 ret->name = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]914 if ((!strcmp(cur->name, "Email")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]915 ret->email = xmlNodeListGetString(doc, cur->childs, 1);
916 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]917 }
918
919 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]920}</pre>
921
922<p>Here is a couple of things to notice:</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]923<ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]924 <li>Usually a recursive parsing style is the more convenient one, XML data
925 being by nature subject to repetitive constructs and usualy exibit highly
926 stuctured patterns.</li>
927 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e.
928 the pointer to the global XML document and the namespace reserved to the
929 application. Document wide information are needed for example to decode
930 entities and it's a good coding practice to define a namespace for your
931 application set of data and test that the element and attributes you're
932 analyzing actually pertains to your application space. This is done by a
933 simple equality test (cur->ns == ns).</li>
934 <li>To retrieve text and attributes value, it is suggested to use the
935 function <em>xmlNodeListGetString</em> to gather all the text and entity
936 reference nodes generated by the DOM output and produce an single text
937 string.</li>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]938</ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]939
940<p>Here is another piece of code used to parse another level of the
941structure:</p>
942<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]943 * a Description for a Job
944 */
945typedef struct job {
946 char *projectID;
947 char *application;
948 char *category;
949 personPtr contact;
950 int nbDevelopers;
951 personPtr developers[100]; /* using dynamic alloc is left as an exercise */
952} job, *jobPtr;
953
954/*
955 * And the code needed to parse it
956 */
957jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
958 jobPtr ret = NULL;
959
960DEBUG("parseJob\n");
961 /*
962 * allocate the struct
963 */
964 ret = (jobPtr) malloc(sizeof(job));
965 if (ret == NULL) {
966 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]967 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]968 }
969 memset(ret, 0, sizeof(job));
970
971 /* We don't care what the top level element name is */
972 cur = cur->childs;
973 while (cur != NULL) {
974
975 if ((!strcmp(cur->name, "Project")) &amp;&amp; (cur->ns == ns)) {
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]976 ret->projectID = xmlGetProp(cur, "ID");
977 if (ret->projectID == NULL) {
978 fprintf(stderr, "Project has no ID\n");
979 }
980 }
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]981 if ((!strcmp(cur->name, "Application")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]982 ret->application = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]983 if ((!strcmp(cur->name, "Category")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]984 ret->category = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]985 if ((!strcmp(cur->name, "Contact")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]986 ret->contact = parsePerson(doc, ns, cur);
987 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]988 }
989
990 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]991}</pre>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]992
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]993<p>One can notice that once used to it, writing this kind of code is quite
994simple, but boring. Ultimately, it could be possble to write stubbers taking
995either C data structure definitions, a set of XML examples or an XML DTD and
996produce the code needed to import and export the content between C data and
997XML storage. This is left as an exercise to the reader :-)</p>
998
999<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]1000example</a> as a template, it is also available with Makefile in the Gnome CVS
1001base under gnome-xml/example</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]1002
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]1003<p></p>
1004
1005<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>
1006
Daniel Veillardda07c342000-01-25 18:31:22 +0000[diff] [blame^]1007<p>$Id: xml.html,v 1.22 2000/01/18 18:01:01 veillard Exp $</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]1008</body>
1009</html>