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blob: ebf534bb3590e5e69fe48c5cbd6657931b209491 [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>
Daniel Veillarde41f2b72000-01-30 20:00:07 +0000[diff] [blame^]152</ul>
153
154<h3>1.8.6: Jan 31 2000</h3>
155<ul>
156 <li>added a nanoFTP transport module, debugged until the new version of <a
157 href="http://rpmfind.net/linux/rpm2html/rpmfind.html">rpmfind</a> can use
158 it without troubles</li>
Daniel Veillardda07c342000-01-25 18:31:22 +0000[diff] [blame]159</ul>
160
161<h3>1.8.5: Jan 21 2000</h3>
162<ul>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]163 <li>adding APIs to parse a well balanced chunk of XML (production <a
164 href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the XML
165 spec)</li>
Daniel Veillard461a66c2000-01-18 18:01:01 +0000[diff] [blame]166 <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li>
167 <li>Jody Goldberg &lt;jgoldberg@home.com> provided another patch trying to
168 solve the zlib checks problems</li>
169 <li>The current state in gnome CVS base is expected to ship as 1.8.5 with
170 gnumeric soon</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]171</ul>
172
173<h3>1.8.4: Jan 13 2000</h3>
174<ul>
175 <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li>
176 <li>all exit() call should have been removed from libxml</li>
177 <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li>
178 <li>added newDocFragment()</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]179</ul>
180
181<h3>1.8.3: Jan 5 2000</h3>
182<ul>
183 <li>a Push interface for the XML and HTML parsers</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]184 <li>an shell like interface to the document tree (try tester --shell
185 :-)</li>
Daniel Veillarddbfd6411999-12-28 16:35:14 +0000[diff] [blame]186 <li>lots of bug fixes and improvement added over XMas hollidays</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]187 <li>fixed the DTD parsing code to work with the xhtml DTD</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]188 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li>
189 <li>Fixed bugs in xmlNewNs()</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]190 <li>External entity loading code has been revamped, now it uses
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]191 xmlLoadExternalEntity(), some fix on entities processing were added</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]192 <li>cleaned up WIN32 includes of socket stuff</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]193</ul>
194
195<h3>1.8.2: Dec 21 1999</h3>
196<ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]197 <li>I got another problem with includes and C++, I hope this issue is fixed
198 for good this time</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]199 <li>Added a few tree modification functions: xmlReplaceNode,
200 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and
201 xmlDocSetRootElement</li>
202 <li>Tried to improve the HTML output with help from <a
203 href="mailto:clahey@umich.edu">Chris Lahey</a></li>
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]204</ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]205
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]206<h3>1.8.1: Dec 18 1999</h3>
207<ul>
208 <li>various patches to avoid troubles when using libxml with C++ compilers
209 the "namespace" keyword and C escaping in include files</li>
210 <li>a problem in one of the core macros IS_CHAR was corrected</li>
211 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing,
212 and more specifically the Dia application</li>
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]213 <li>fixed a posteriori validation (validation after parsing, or by using a
214 Dtd not specified in the original document)</li>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]215 <li>fixed a bug in</li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]216</ul>
217
218<h3>1.8.0: Dec 12 1999</h3>
219<ul>
220 <li>cleanup, especially memory wise</li>
221 <li>the parser should be more reliable, especially the HTML one, it should
222 not crash, whatever the input !</li>
223 <li>Integrated various patches, especially a speedup improvement for large
224 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>,
225 configure with --with-buffers to enable them.</li>
226 <li>attribute normalization, oops should have been added long ago !</li>
227 <li>attributes defaulted from Dtds should be available, xmlSetProp() now
228 does entities escapting by default.</li>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]229</ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]230
231<h3>1.7.4: Oct 25 1999</h3>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]232<ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]233 <li>Lots of HTML improvement</li>
234 <li>Fixed some errors when saving both XML and HTML</li>
235 <li>More examples, the regression tests should now look clean</li>
236 <li>Fixed a bug with contiguous charref</li>
237</ul>
238
239<h3>1.7.3: Sep 29 1999</h3>
240<ul>
241 <li>portability problems fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]242 <li>snprintf was used unconditionnally, leading to link problems on system
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]243 were it's not available, fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]244</ul>
245
246<h3>1.7.1: Sep 24 1999</h3>
247<ul>
248 <li>The basic type for strings manipulated by libxml has been renamed in
249 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason
250 is that CHAR was conflicting with a predefined type on Windows. However on
251 non WIN32 environment, compatibility is provided by the way of a
252 <strong>#define </strong>.</li>
253 <li>Changed another error : the use of a structure field called errno, and
254 leading to troubles on platforms where it's a macro</li>
255</ul>
256
257<h3>1.7.0: sep 23 1999</h3>
258<ul>
259 <li>Added the ability to fetch remote DTD or parsed entities, see the <a
260 href="gnome-xml-nanohttp.html">nanohttp</a> module.</li>
261 <li>Added an errno to report errors by another mean than a simple printf
262 like callback</li>
263 <li>Finished ID/IDREF support and checking when validation</li>
264 <li>Serious memory leaks fixed (there is now a <a
265 href="gnome-xml-xmlmemory.html">memory wrapper</a> module)</li>
266 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a>
267 implementation</li>
268 <li>Added an HTML parser front-end</li>
269</ul>
270
271<h2><a name="XML">XML</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]272
273<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for markup
274based structured documents, here is <a name="example">an example</a>:</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]275<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]276&lt;EXAMPLE prop1="gnome is great" prop2="&amp;amp; linux too">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]277 &lt;head>
278 &lt;title>Welcome to Gnome&lt;/title>
279 &lt;/head>
280 &lt;chapter>
281 &lt;title>The Linux adventure&lt;/title>
282 &lt;p>bla bla bla ...&lt;/p>
283 &lt;image href="linus.gif"/>
284 &lt;p>...&lt;/p>
285 &lt;/chapter>
286&lt;/EXAMPLE></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]287
288<p>The first line specify that it's an XML document and gives useful
289informations about it's encoding. Then the document is a text format whose
290structure is specified by tags between brackets. <strong>Each tag opened have
291to be closed</strong> XML is pedantic about this, not that for example the
292image tag has no content (just an attribute) and is closed by ending up the
293tag with <code>/></code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]294
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]295<p>XML can be applied sucessfully to a wide range or usage from long term
296structured document maintenance where it follows the steps of SGML to simple
297data encoding mechanism like configuration file format (glade), spreadsheets
298(gnumeric), or even shorter lived document like in WebDAV where it is used to
299encode remote call between a client and a server.</p>
300
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]301<h2><a name="tree">The tree output</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]302
303<p>The parser returns a tree built during the document analysis. The value
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]304returned is an <strong>xmlDocPtr</strong> (i.e. a pointer to an
305<strong>xmlDoc</strong> structure). This structure contains informations like
306the file name, the document type, and a <strong>root</strong> pointer which
307is the root of the document (or more exactly the first child under the root
308which is the document). The tree is made of <strong>xmlNode</strong>s, chained
309in double linked lists of siblings and with childs&lt;->parent relationship.
310An xmlNode can also carry properties (a chain of xmlAttr structures). An
311attribute 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]312
313<p>Here is an example (erroneous w.r.t. the XML spec since there should be
314only one ELEMENT under the root):</p>
315
316<p><img src="structure.gif" alt=" structure.gif "></p>
317
318<p>In the source package there is a small program (not installed by default)
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]319called <strong>tester</strong> which parses XML files given as argument and
320prints them back as parsed, this is useful to detect errors both in XML code
321and in the XML parser itself. It has an option <strong>--debug</strong> which
322prints the actual in-memory structure of the document, here is the result with
323the <a href="#example">example</a> given before:</p>
324<pre>DOCUMENT
325version=1.0
326standalone=true
327 ELEMENT EXAMPLE
328 ATTRIBUTE prop1
329 TEXT
330 content=gnome is great
331 ATTRIBUTE prop2
332 ENTITY_REF
333 TEXT
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]334 content= linux too
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]335 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]336 TEXT
337 content=Welcome to Gnome
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]338 ELEMENT chapter
339 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]340 TEXT
341 content=The Linux adventure
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]342 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]343 TEXT
344 content=bla bla bla ...
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]345 ELEMENT image
346 ATTRIBUTE href
347 TEXT
348 content=linus.gif
349 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]350 TEXT
351 content=...</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]352
353<p>This should be useful to learn the internal representation model.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]354
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]355<h2><a name="interface">The SAX interface</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]356
357<p>Sometimes the DOM tree output is just to large to fit reasonably into
358memory. In that case and if you don't expect to save back the XML document
359loaded using libxml, it's better to use the SAX interface of libxml. SAX is a
360<strong>callback based interface</strong> to the parser. Before parsing, the
361application layer register a customized set of callbacks which will be called
362by the library as it progresses through the XML input.</p>
363
364<p>To get a more detailed step-by-step guidance on using the SAX interface of
365libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> made <a
366href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice
367documentation.</a></p>
368
369<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
370program located in the gnome-xml module (it's usually not shipped in the
371binary packages of libxml, but you can also find it in the tar source
372distribution). Here is the sequence of callback that would be generated when
373parsing the example given before as reported by testSAX:</p>
374<pre>SAX.setDocumentLocator()
375SAX.startDocument()
376SAX.getEntity(amp)
377SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp;amp; linux too')
378SAX.characters( , 3)
379SAX.startElement(head)
380SAX.characters( , 4)
381SAX.startElement(title)
382SAX.characters(Welcome to Gnome, 16)
383SAX.endElement(title)
384SAX.characters( , 3)
385SAX.endElement(head)
386SAX.characters( , 3)
387SAX.startElement(chapter)
388SAX.characters( , 4)
389SAX.startElement(title)
390SAX.characters(The Linux adventure, 19)
391SAX.endElement(title)
392SAX.characters( , 4)
393SAX.startElement(p)
394SAX.characters(bla bla bla ..., 15)
395SAX.endElement(p)
396SAX.characters( , 4)
397SAX.startElement(image, href='linus.gif')
398SAX.endElement(image)
399SAX.characters( , 4)
400SAX.startElement(p)
401SAX.characters(..., 3)
402SAX.endElement(p)
403SAX.characters( , 3)
404SAX.endElement(chapter)
405SAX.characters( , 1)
406SAX.endElement(EXAMPLE)
407SAX.endDocument()</pre>
408
409<p>Most of the other functionnalities of libxml are based on the DOM tree
410building facility, so nearly everything up to the end of this document
411presuppose the use of the standard DOM tree build. Note that the DOM tree
412itself is built by a set of registered default callbacks, without internal
413specific interface.</p>
414
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]415<h2><a name="library">The XML library interfaces</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]416
417<p>This section is directly intended to help programmers getting bootstrapped
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]418using the XML library from the C language. It doesn't intent to be extensive,
419I hope the automatically generated docs will provide the completeness
420required, but as a separated set of documents. The interfaces of the XML
421library are by principle low level, there is nearly zero abstration. Those
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]422interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]423
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]424<p>The <a href="gnome-xml-parser.html">parser interfaces for XML</a> are
425separated from the <a href="gnome-xml-htmlparser.html">HTML parser ones</a>,
426let's have a look at how it can be called:</p>
427
428<h3><a name="Invoking">Invoking the parser : the pull way</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]429
430<p>Usually, the first thing to do is to read an XML input, the parser accepts
431to parse both memory mapped documents or direct files. The functions are
432defined in "parser.h":</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]433<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]434 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
435 <dd><p>parse a zero terminated string containing the document</p>
436 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]437</dl>
438<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]439 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
440 <dd><p>parse an XML document contained in a file (possibly compressed)</p>
441 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]442</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]443
444<p>This returns a pointer to the document structure (or NULL in case of
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]445failure).</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]446
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]447<h3 id="Invoking1">Invoking the parser: the push way</h3>
448
449<p>In order for the application to keep the control when the document is been
450fetched (common for GUI based programs) the libxml, as of version 1.8.3
451provides a push interface too, here are the interfaces:</p>
452<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
453 void *user_data,
454 const char *chunk,
455 int size,
456 const char *filename);
457int xmlParseChunk (xmlParserCtxtPtr ctxt,
458 const char *chunk,
459 int size,
460 int terminate);</pre>
461
462<p>and here is a simple use example:</p>
463<pre> FILE *f;
464
465 f = fopen(filename, "r");
466 if (f != NULL) {
467 int res, size = 1024;
468 char chars[1024];
469 xmlParserCtxtPtr ctxt;
470
471 res = fread(chars, 1, 4, f);
472 if (res > 0) {
473 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
474 chars, res, filename);
475 while ((res = fread(chars, 1, size, f)) > 0) {
476 xmlParseChunk(ctxt, chars, res, 0);
477 }
478 xmlParseChunk(ctxt, chars, 0, 1);
479 doc = ctxt->myDoc;
480 xmlFreeParserCtxt(ctxt);
481 }
482 }</pre>
483
484<p>Also note that the HTML parser embedded into libxml also have a push
485interface they are just prefixed by "html" instead of "xml"</p>
486
487<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
488
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]489<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]490memory-hungry, first to load the document in memory, second to build the tree.
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]491Reading a document without building the tree is possible using the SAX
492interfaces (see SAX.h and <a
493href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
494Henstridge documentation</a>), not also that the push interface can be limited
495to SAX, just use the two first arguments of
496<code>xmlCreatePushParserCtxt()</code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]497
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]498<h3><a name="Building">Building a tree from scratch</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]499
500<p>The other way to get an XML tree in memory is by building it. Basically
501there is a set of functions dedicated to building new elements, those are also
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]502described in "tree.h", here is for example the piece of code producing the
503example used before:</p>
504<pre> xmlDocPtr doc;
505 xmlNodePtr tree, subtree;
506
507 doc = xmlNewDoc("1.0");
508 doc->root = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
509 xmlSetProp(doc->root, "prop1", "gnome is great");
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]510 xmlSetProp(doc->root, "prop2", "&amp; linux too");
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]511 tree = xmlNewChild(doc->root, NULL, "head", NULL);
512 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
513 tree = xmlNewChild(doc->root, NULL, "chapter", NULL);
514 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
515 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
516 subtree = xmlNewChild(tree, NULL, "image", NULL);
517 xmlSetProp(subtree, "href", "linus.gif");</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]518
519<p>Not really rocket science ...</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]520
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]521<h3><a name="Traversing">Traversing the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]522
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]523<p>Basically by <a href="gnome-xml-tree.html">including "tree.h"</a> your code
524has access to the internal structure of all the element of the tree. The names
525should be somewhat simple like <strong>parent</strong>,
526<strong>childs</strong>, <strong>next</strong>, <strong>prev</strong>,
527<strong>properties</strong>, etc... For example still with the previous
528example:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]529<pre><code>doc->root->childs->childs</code></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]530
531<p>points to the title element,</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]532<pre>doc->root->childs->next->child->child</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]533
534<p>points to the text node containing the chapter titlle "The Linux adventure"
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]535and</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]536
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]537<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
538present before the document root, so doc->root may point to an element which
539is not the document Root Element, a function
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]540<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]541
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]542<h3><a name="Modifying">Modifying the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]543
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]544<p>functions are provided to read and write the document content, here is an
545excerpt from the <a href="gnome-xml-tree.html">tree API</a>:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]546<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]547 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
548 xmlChar *value);</code></dt>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]549 <dd><p>This set (or change) an attribute carried by an ELEMENT node the
550 value can be NULL</p>
551 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]552</dl>
553<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]554 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]555 *name);</code></dt>
556 <dd><p>This function returns a pointer to the property content, note that
557 no extra copy is made</p>
558 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]559</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]560
561<p>Two functions must be used to read an write the text associated to
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]562elements:</p>
563<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]564 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]565 *value);</code></dt>
566 <dd><p>This function takes an "external" string and convert it to one text
567 node or possibly to a list of entity and text nodes. All non-predefined
568 entity references like &amp;Gnome; will be stored internally as an
569 entity node, hence the result of the function may not be a single
570 node.</p>
571 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]572</dl>
573<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]574 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]575 inLine);</code></dt>
576 <dd><p>this is the dual function, which generate a new string containing
577 the content of the text and entity nodes. Note the extra argument
578 inLine, if set to 1 instead of returning the &amp;Gnome; XML encoding in
579 the string it will substitute it with it's value say "GNU Network Object
580 Model Environment". Set it if you want to use the string for non XML
581 usage like User Interface.</p>
582 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]583</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]584
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]585<h3><a name="Saving">Saving a tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]586
587<p>Basically 3 options are possible:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]588<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]589 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]590 *size);</code></dt>
591 <dd><p>returns a buffer where the document has been saved</p>
592 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]593</dl>
594<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]595 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
596 <dd><p>dumps a buffer to an open file descriptor</p>
597 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]598</dl>
599<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]600 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
601 <dd><p>save the document ot a file. In that case the compression interface
602 is triggered if turned on</p>
603 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]604</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]605
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]606<h3><a name="Compressio">Compression</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]607
608<p>The library handle transparently compression when doing file based
609accesses, the level of compression on saves can be tuned either globally or
610individually for one file:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]611<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]612 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
613 <dd><p>Get the document compression ratio (0-9)</p>
614 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]615</dl>
616<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]617 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
618 <dd><p>Set the document compression ratio</p>
619 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]620</dl>
621<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]622 <dt><code>int xmlGetCompressMode(void);</code></dt>
623 <dd><p>Get the default compression ratio</p>
624 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]625</dl>
626<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]627 <dt><code>void xmlSetCompressMode(int mode);</code></dt>
628 <dd><p>set the default compression ratio</p>
629 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]630</dl>
631
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]632<h2><a name="Entities">Entities or no entities</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]633
634<p>Entities principle is similar to simple C macros. They define an
635abbreviation for a given string that you can reuse many time through the
636content of your document. They are especially useful when frequent occurrences
637of a given string may occur within a document or to confine the change needed
638to a document to a restricted area in the internal subset of the document (at
639the beginning). Example:</p>
640<pre>1 &lt;?xml version="1.0"?>
6412 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
6423 &lt;!ENTITY xml "Extensible Markup Language">
6434 ]>
6445 &lt;EXAMPLE>
6456 &amp;xml;
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]6467 &lt;/EXAMPLE></pre>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]647
648<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]649it's name with '&amp;' and following it by ';' without any spaces added. There
650are 5 predefined entities in libxml allowing to escape charaters with
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]651predefined meaning in some parts of the xml document content:
652<strong>&amp;lt;</strong> for the letter '&lt;', <strong>&amp;gt;</strong> for
653the letter '>', <strong>&amp;apos;</strong> for the letter ''',
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]654<strong>&amp;quot;</strong> for the letter '"', and <strong>&amp;amp;</strong>
655for the letter '&amp;'.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]656
657<p>One of the problems related to entities is that you may want the parser to
658substitute entities content to see the replacement text in your application,
659or you may prefer keeping entities references as such in the content to be
660able to save the document back without loosing this usually precious
661information (if the user went through the pain of explicitley defining
662entities, he may have a a rather negative attitude if you blindly susbtitute
663them as saving time). The function <a
664href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
665allows to check and change the behaviour, which is to not substitute entities
666by default.</p>
667
668<p>Here is the DOM tree built by libxml for the previous document in the
669default case:</p>
670<pre>/gnome/src/gnome-xml -> ./tester --debug test/ent1
671DOCUMENT
672version=1.0
673 ELEMENT EXAMPLE
674 TEXT
675 content=
676 ENTITY_REF
677 INTERNAL_GENERAL_ENTITY xml
678 content=Extensible Markup Language
679 TEXT
680 content=</pre>
681
682<p>And here is the result when substituting entities:</p>
683<pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
684DOCUMENT
685version=1.0
686 ELEMENT EXAMPLE
687 TEXT
688 content= Extensible Markup Language</pre>
689
690<p>So entities or no entities ? Basically it depends on your use case, I
691suggest to keep the non-substituting default behaviour and avoid using
692entities in your XML document or data if you are not willing to handle the
693entity references elements in the DOM tree.</p>
694
695<p>Note that at save time libxml enforce the conversion of the predefined
696entities where necessary to prevent well-formedness problems, and will also
697transparently replace those with chars (i.e. will not generate entity
698reference elements in the DOM tree nor call the reference() SAX callback when
699finding them in the input).</p>
700
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]701<h2><a name="Namespaces">Namespaces</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]702
703<p>The libxml library implement namespace @@ support by recognizing namespace
704contructs in the input, and does namespace lookup automatically when building
705the DOM tree. A namespace declaration is associated with an in-memory
706structure and all elements or attributes within that namespace point to it.
707Hence testing the namespace is a simple and fast equality operation at the
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]708user level.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]709
710<p>I suggest it that people using libxml use a namespace, and declare it on
711the root element of their document as the default namespace. Then they dont
712need to happend the prefix in the content but we will have a basis for future
713semantic refinement and merging of data from different sources. This doesn't
714augment significantly the size of the XML output, but significantly increase
715it's value in the long-term.</p>
716
717<p>Concerning the namespace value, this has to be an URL, but this doesn't
718have to point to any existing resource on the Web. I suggest using an URL
719within a domain you control, which makes sense and if possible holding some
720kind of versionning informations. For example
721<code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme.
722Then when you load a file, make sure that a namespace carrying the
723version-independant prefix is installed on the root element of your document,
724and if the version information don't match something you know, warn the user
725and be liberal in what you accept as the input. Also do *not* try to base
726namespace checking on the prefix value &lt;foo:text> may be exactly the same
727as &lt;bar:text> in another document, what really matter is the URI
728associated with the element or the attribute, not the prefix string which is
729just a shortcut for the full URI.</p>
730
731<p>@@Interfaces@@</p>
732
733<p>@@Examples@@</p>
734
735<p>Usually people object using namespace in the case of validation, I object
736this and will make sure that using namespaces won't break validity checking,
737so even is you plan or are using validation I strongly suggest to add
738namespaces to your document. A default namespace scheme
739<code>xmlns="http://...."</code> should not break validity even on less
740flexible parsers. Now using namespace to mix and differenciate content coming
741from mutliple Dtd will certainly break current validation schemes, I will try
742to provide ways to do this, but this may not be portable or standardized.</p>
743
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]744<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]745
746<p>Well what is validation and what is a DTD ?</p>
747
748<p>Validation is the process of checking a document against a set of
749construction rules, a <strong>DTD</strong> (Document Type Definition) is such
750a set of rules.</p>
751
752<p>The validation process and building DTDs are the two most difficult parts
753of XML life cycle. Briefly a DTD defines all the possibles element to be
754found within your document, what is the formal shape of your document tree (by
755defining the allowed content of an element, either text, a regular expression
756for the allowed list of children, or mixed content i.e. both text and childs).
757The DTD also defines the allowed attributes for all elements and the types of
758the attributes. For more detailed informations, I suggest to read the related
759parts of the XML specification, the examples found under
760gnome-xml/test/valid/dtd and the large amount of books available on XML. The
761dia example in gnome-xml/test/valid should be both simple and complete enough
762to allow you to build your own.</p>
763
764<p>A word of warning, building a good DTD which will fit your needs of your
765application in the long-term is far from trivial, however the extra level of
766quality it can insure is well worth the price for some sets of applications or
767if you already have already a DTD defined for your application field.</p>
768
769<p>The validation is not completely finished but in a (very IMHO) usable
770state. Until a real validation interface is defined the way to do it is to
771define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external
772variable to 1, this will of course be changed at some point:</p>
773
774<p>extern int xmlDoValidityCheckingDefaultValue;</p>
775
776<p>...</p>
777
778<p>xmlDoValidityCheckingDefaultValue = 1;</p>
779
780<p></p>
781
782<p>To handle external entities, use the function
783<strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to
784link in you HTTP/FTP/Entities database library to the standard libxml
785core.</p>
786
787<p>@@interfaces@@</p>
788
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]789<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]790
791<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]792Model</em> this is an API for accessing XML or HTML structured documents.
793Native 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]794be based on gnome-xml. This will be a far cleaner interface to manipulate XML
Daniel Veillardc08a2c61999-09-08 21:35:25 +0000[diff] [blame]795files within Gnome since it won't expose the internal structure. DOM defines a
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]796set of IDL (or Java) interfaces allowing to traverse and manipulate a
797document. The DOM library will allow accessing and modifying "live" documents
798presents on other programs like this:</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]799
800<p><img src="DOM.gif" alt=" DOM.gif "></p>
801
802<p>This should help greatly doing things like modifying a gnumeric spreadsheet
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]803embedded in a GWP document for example.</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]804
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]805<p>The current DOM implementation on top of libxml is the <a
806href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module</a>, this is
807a full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph
808Levien</a>.</p>
809
810<p>The gnome-dom module in the Gnome CVS base is obsolete</p>
811
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]812<h2><a name="Example"></a><a name="real">A real example</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]813
814<p>Here is a real size example, where the actual content of the application
815data 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]816a proposal to keep a database of jobs related to Gnome, with an XML based
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]817storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
818base</a>:</p>
819<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]820&lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
821 &lt;gjob:Jobs>
822
823 &lt;gjob:Job>
824 &lt;gjob:Project ID="3"/>
825 &lt;gjob:Application>GBackup&lt;/gjob:Application>
826 &lt;gjob:Category>Development&lt;/gjob:Category>
827
828 &lt;gjob:Update>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]829 &lt;gjob:Status>Open&lt;/gjob:Status>
830 &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]831 &lt;gjob:Salary>USD 0.00&lt;/gjob:Salary>
832 &lt;/gjob:Update>
833
834 &lt;gjob:Developers>
835 &lt;gjob:Developer>
836 &lt;/gjob:Developer>
837 &lt;/gjob:Developers>
838
839 &lt;gjob:Contact>
840 &lt;gjob:Person>Nathan Clemons&lt;/gjob:Person>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]841 &lt;gjob:Email>nathan@windsofstorm.net&lt;/gjob:Email>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]842 &lt;gjob:Company>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]843 &lt;/gjob:Company>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]844 &lt;gjob:Organisation>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]845 &lt;/gjob:Organisation>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]846 &lt;gjob:Webpage>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]847 &lt;/gjob:Webpage>
848 &lt;gjob:Snailmail>
849 &lt;/gjob:Snailmail>
850 &lt;gjob:Phone>
851 &lt;/gjob:Phone>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]852 &lt;/gjob:Contact>
853
854 &lt;gjob:Requirements>
855 The program should be released as free software, under the GPL.
856 &lt;/gjob:Requirements>
857
858 &lt;gjob:Skills>
859 &lt;/gjob:Skills>
860
861 &lt;gjob:Details>
862 A GNOME based system that will allow a superuser to configure
863 compressed and uncompressed files and/or file systems to be backed
864 up with a supported media in the system. This should be able to
865 perform via find commands generating a list of files that are passed
866 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
867 or via operations performed on the filesystem itself. Email
868 notification and GUI status display very important.
869 &lt;/gjob:Details>
870
871 &lt;/gjob:Job>
872
873 &lt;/gjob:Jobs>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]874&lt;/gjob:Helping></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]875
876<p>While loading the XML file into an internal DOM tree is a matter of calling
877only a couple of functions, browsing the tree to gather the informations and
878generate the internals structures is harder, and more error prone.</p>
879
880<p>The suggested principle is to be tolerant with respect to the input
881structure. For example the ordering of the attributes is not significant, Cthe
882XML specification is clear about it. It's also usually a good idea to not be
883dependant of the orders of the childs of a given node, unless it really makes
884things harder. Here is some code to parse the informations for a person:</p>
885<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]886 * A person record
887 */
888typedef struct person {
889 char *name;
890 char *email;
891 char *company;
892 char *organisation;
893 char *smail;
894 char *webPage;
895 char *phone;
896} person, *personPtr;
897
898/*
899 * And the code needed to parse it
900 */
901personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
902 personPtr ret = NULL;
903
904DEBUG("parsePerson\n");
905 /*
906 * allocate the struct
907 */
908 ret = (personPtr) malloc(sizeof(person));
909 if (ret == NULL) {
910 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]911 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]912 }
913 memset(ret, 0, sizeof(person));
914
915 /* We don't care what the top level element name is */
916 cur = cur->childs;
917 while (cur != NULL) {
918 if ((!strcmp(cur->name, "Person")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]919 ret->name = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]920 if ((!strcmp(cur->name, "Email")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]921 ret->email = xmlNodeListGetString(doc, cur->childs, 1);
922 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]923 }
924
925 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]926}</pre>
927
928<p>Here is a couple of things to notice:</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]929<ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]930 <li>Usually a recursive parsing style is the more convenient one, XML data
931 being by nature subject to repetitive constructs and usualy exibit highly
932 stuctured patterns.</li>
933 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e.
934 the pointer to the global XML document and the namespace reserved to the
935 application. Document wide information are needed for example to decode
936 entities and it's a good coding practice to define a namespace for your
937 application set of data and test that the element and attributes you're
938 analyzing actually pertains to your application space. This is done by a
939 simple equality test (cur->ns == ns).</li>
940 <li>To retrieve text and attributes value, it is suggested to use the
941 function <em>xmlNodeListGetString</em> to gather all the text and entity
942 reference nodes generated by the DOM output and produce an single text
943 string.</li>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]944</ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]945
946<p>Here is another piece of code used to parse another level of the
947structure:</p>
948<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]949 * a Description for a Job
950 */
951typedef struct job {
952 char *projectID;
953 char *application;
954 char *category;
955 personPtr contact;
956 int nbDevelopers;
957 personPtr developers[100]; /* using dynamic alloc is left as an exercise */
958} job, *jobPtr;
959
960/*
961 * And the code needed to parse it
962 */
963jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
964 jobPtr ret = NULL;
965
966DEBUG("parseJob\n");
967 /*
968 * allocate the struct
969 */
970 ret = (jobPtr) malloc(sizeof(job));
971 if (ret == NULL) {
972 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]973 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]974 }
975 memset(ret, 0, sizeof(job));
976
977 /* We don't care what the top level element name is */
978 cur = cur->childs;
979 while (cur != NULL) {
980
981 if ((!strcmp(cur->name, "Project")) &amp;&amp; (cur->ns == ns)) {
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]982 ret->projectID = xmlGetProp(cur, "ID");
983 if (ret->projectID == NULL) {
984 fprintf(stderr, "Project has no ID\n");
985 }
986 }
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]987 if ((!strcmp(cur->name, "Application")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]988 ret->application = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]989 if ((!strcmp(cur->name, "Category")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]990 ret->category = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]991 if ((!strcmp(cur->name, "Contact")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]992 ret->contact = parsePerson(doc, ns, cur);
993 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]994 }
995
996 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]997}</pre>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]998
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]999<p>One can notice that once used to it, writing this kind of code is quite
1000simple, but boring. Ultimately, it could be possble to write stubbers taking
1001either C data structure definitions, a set of XML examples or an XML DTD and
1002produce the code needed to import and export the content between C data and
1003XML storage. This is left as an exercise to the reader :-)</p>
1004
1005<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]1006example</a> as a template, it is also available with Makefile in the Gnome CVS
1007base under gnome-xml/example</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]1008
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]1009<p></p>
1010
1011<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>
1012
Daniel Veillarde41f2b72000-01-30 20:00:07 +0000[diff] [blame^]1013<p>$Id: xml.html,v 1.23 2000/01/25 18:31:22 veillard Exp $</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]1014</body>
1015</html>