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| <h1 align="center">The XML library for Gnome</h1> |
| |
| <h2 style="text-align: center">libxml, a.k.a. gnome-xml</h2> |
| |
| <p></p> |
| <ul> |
| <li><a href="#Introducti">Introduction</a></li> |
| <li><a href="#Documentat">Documentation</a></li> |
| <li><a href="#Downloads">Downloads</a></li> |
| <li><a href="#News">News</a></li> |
| <li><a href="#XML">XML</a></li> |
| <li><a href="#tree">The tree output</a></li> |
| <li><a href="#interface">The SAX interface</a></li> |
| <li><a href="#library">The XML library interfaces</a> |
| <ul> |
| <li><a href="#Invoking">Invoking the parser: the pull way</a></li> |
| <li><a href="#Invoking">Invoking the parser: the push way</a></li> |
| <li><a href="#Invoking2">Invoking the parser: the SAX interface</a></li> |
| <li><a href="#Building">Building a tree from scratch</a></li> |
| <li><a href="#Traversing">Traversing the tree</a></li> |
| <li><a href="#Modifying">Modifying the tree</a></li> |
| <li><a href="#Saving">Saving the tree</a></li> |
| <li><a href="#Compressio">Compression</a></li> |
| </ul> |
| </li> |
| <li><a href="#Entities">Entities or no entities</a></li> |
| <li><a href="#Namespaces">Namespaces</a></li> |
| <li><a href="#Validation">Validation</a></li> |
| <li><a href="#Principles">DOM principles</a></li> |
| <li><a href="#real">A real example</a></li> |
| </ul> |
| |
| <h2><a name="Introducti">Introduction</a></h2> |
| |
| <p>This document describes the <a href="http://www.w3.org/XML/">XML</a> |
| library provideed in the <a href="http://www.gnome.org/">Gnome</a> framework. |
| XML is a standard to build tag based structured documents/data.</p> |
| |
| <p>Here are some key points about libxml:</p> |
| <ul> |
| <li>The internal document repesentation is as close as possible to the <a |
| href="http://www.w3.org/DOM/">DOM</a> interfaces.</li> |
| <li>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX |
| like interface</a>, the interface is designed to be compatible with <a |
| href="http://www.jclark.com/xml/expat.html">Expat</a> one.</li> |
| <li>Libxml now include a nearly complete <a |
| href="http://www.w3.org/TR/xpath">XPath</a> implementation.</li> |
| <li>Libxml export Push and Pull type parser interface for both XML and |
| HTML.</li> |
| <li>This library is released both under the W3C Copyright and the GNU LGPL, |
| basically everybody should be happy, if not, drop me a mail.</li> |
| </ul> |
| |
| <h2><a name="Documentat">Documentation</a></h2> |
| |
| <p>There is some on-line resources about using libxml :</p> |
| <ol> |
| <li>The code is commented in a way which allow <a |
| href="http://xmlsoft.org/libxml.html">extensive documentation</a> to be |
| automatically extracted.</li> |
| <li>This page provides a global overview and <a href="#real">some |
| examples</a> on how to use libxml</li> |
| <li><a href="mailto:james@daa.com.au">James Henstridge</a> made <a |
| href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice |
| documentation</a> expaining how to use the SAX interface of libxml</li> |
| <li>George Lebl wrote <a |
| href="http://www-4.ibm.com/software/developer/library/gnome3/">an article |
| for IBM developperWorks</a> about using libxml</li> |
| <li>It is also a good idea to check to <a href="mailto:raph@levien.com">Raph |
| Levien</a> <a href="http://levien.com/gnome/">web site</a> since he is |
| building the <a href="http://levien.com/gnome/gdome.html">DOM interface |
| gdome</a> on top of libxml result tree and an implementation of <a |
| href="http://www.w3.org/Graphics/SVG/">SVG</a> called <a |
| href="http://www.levien.com/svg/">gill</a>. Check his <a |
| href="http://www.levien.com/gnome/domination.html">DOMination |
| paper</a>.</li> |
| <li>And don't forget to look at the <a href="/messages/">mailing-list |
| archive</a> too.</li> |
| </ol> |
| |
| <h3>Reporting bugs and getting help</h3> |
| |
| <p>Well bugs or missing features are always possible, and I will make a point |
| of fixing them in a timely fashion. The best way it to <a |
| href="http://bugs.gnome.org/db/pa/lgnome-xml.html">use the Gnome bug tracking |
| database</a>. I look at reports there regulary and it's good to have a |
| reminder when a bug is still open. Check the <a |
| href="http://bugs.gnome.org/Reporting.html">instructions on reporting bugs</a> |
| and be sure to specify thatthe bug is for the package gnome-xml.</p> |
| |
| <p>There is also a mailing-list <a |
| href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> for libxml, with an <a |
| href="http://xmlsoft.org/messages">on-line archive</a>. To subscribe to this |
| majordomo based list, send a mail to <a |
| href="mailto:majordomo@rufus.w3.org">majordomo@rufus.w3.org</a> with |
| "subscribe xml" in the <strong>content</strong> of the message.</p> |
| |
| <p>Alternately you can just send the bug to the <a |
| href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> list.</p> |
| |
| <h2><a name="Downloads">Downloads</a></h2> |
| |
| <p>Latest versions can be found on <a |
| href="ftp://rpmfind.net/pub/veillard/">rpmfind.net</a> or on the <a |
| href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either |
| as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source |
| archive</a> or <a href="ftp://ftp.gnome.org/pub/GNOME/contrib/rpms/">RPMs |
| packages</a> (NOTE that you need both the <a |
| href="http://rpmfind.net/linux/RPM/libxml.html">libxml</a> and <a |
| href="http://rpmfind.net/linux/RPM/libxml-devel.html">libxml-devel</a> |
| packages installed to compile applications using libxml).</p> |
| |
| <p>Libxml is also available from 2 CVs bases:</p> |
| <ul> |
| <li><p>The <a href="http://dev.w3.org/cvsweb/XML/">W3C CVS base</a>, |
| available read-only using the CVS pserver authentification (I tend to use |
| this base for my own developements so it's updated more regulary, but |
| content may not be as stable):</p> |
| <pre>CVSROOT=:pserver:anonymous@dev.w3.org:/sources/public |
| password: anonymous |
| module: XML</pre> |
| </li> |
| <li><p>The <a |
| href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xml">Gnome |
| CVS base</a>, Check the <a |
| href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> page, |
| the CVS module is <b>gnome-xml</b></p> |
| </li> |
| </ul> |
| |
| <h2><a name="News">News</a></h2> |
| |
| <h3>CVS only : check the <a |
| href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file |
| for really accurate description</h3> |
| <ul> |
| <li>working on HTML and XML links recognition layers, get in touch with me |
| if you want to test those.</li> |
| <li>there is some kind of roadmap to libxml-2.0: fix I18N, and <a |
| href="http://rpmfind.net/tools/gdome/messages/0039.html">change structures |
| to accomodate DOM</a></li> |
| </ul> |
| |
| <h3>1.8.6: Jan 31 2000</h3> |
| <ul> |
| <li>added a nanoFTP transport module, debugged until the new version of <a |
| href="http://rpmfind.net/linux/rpm2html/rpmfind.html">rpmfind</a> can use |
| it without troubles</li> |
| </ul> |
| |
| <h3>1.8.5: Jan 21 2000</h3> |
| <ul> |
| <li>adding APIs to parse a well balanced chunk of XML (production <a |
| href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the XML |
| spec)</li> |
| <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li> |
| <li>Jody Goldberg <jgoldberg@home.com> provided another patch trying to |
| solve the zlib checks problems</li> |
| <li>The current state in gnome CVS base is expected to ship as 1.8.5 with |
| gnumeric soon</li> |
| </ul> |
| |
| <h3>1.8.4: Jan 13 2000</h3> |
| <ul> |
| <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li> |
| <li>all exit() call should have been removed from libxml</li> |
| <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li> |
| <li>added newDocFragment()</li> |
| </ul> |
| |
| <h3>1.8.3: Jan 5 2000</h3> |
| <ul> |
| <li>a Push interface for the XML and HTML parsers</li> |
| <li>an shell like interface to the document tree (try tester --shell |
| :-)</li> |
| <li>lots of bug fixes and improvement added over XMas hollidays</li> |
| <li>fixed the DTD parsing code to work with the xhtml DTD</li> |
| <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li> |
| <li>Fixed bugs in xmlNewNs()</li> |
| <li>External entity loading code has been revamped, now it uses |
| xmlLoadExternalEntity(), some fix on entities processing were added</li> |
| <li>cleaned up WIN32 includes of socket stuff</li> |
| </ul> |
| |
| <h3>1.8.2: Dec 21 1999</h3> |
| <ul> |
| <li>I got another problem with includes and C++, I hope this issue is fixed |
| for good this time</li> |
| <li>Added a few tree modification functions: xmlReplaceNode, |
| xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and |
| xmlDocSetRootElement</li> |
| <li>Tried to improve the HTML output with help from <a |
| href="mailto:clahey@umich.edu">Chris Lahey</a></li> |
| </ul> |
| |
| <h3>1.8.1: Dec 18 1999</h3> |
| <ul> |
| <li>various patches to avoid troubles when using libxml with C++ compilers |
| the "namespace" keyword and C escaping in include files</li> |
| <li>a problem in one of the core macros IS_CHAR was corrected</li> |
| <li>fixed a bug introduced in 1.8.0 breaking default namespace processing, |
| and more specifically the Dia application</li> |
| <li>fixed a posteriori validation (validation after parsing, or by using a |
| Dtd not specified in the original document)</li> |
| <li>fixed a bug in</li> |
| </ul> |
| |
| <h3>1.8.0: Dec 12 1999</h3> |
| <ul> |
| <li>cleanup, especially memory wise</li> |
| <li>the parser should be more reliable, especially the HTML one, it should |
| not crash, whatever the input !</li> |
| <li>Integrated various patches, especially a speedup improvement for large |
| dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>, |
| configure with --with-buffers to enable them.</li> |
| <li>attribute normalization, oops should have been added long ago !</li> |
| <li>attributes defaulted from Dtds should be available, xmlSetProp() now |
| does entities escapting by default.</li> |
| </ul> |
| |
| <h3>1.7.4: Oct 25 1999</h3> |
| <ul> |
| <li>Lots of HTML improvement</li> |
| <li>Fixed some errors when saving both XML and HTML</li> |
| <li>More examples, the regression tests should now look clean</li> |
| <li>Fixed a bug with contiguous charref</li> |
| </ul> |
| |
| <h3>1.7.3: Sep 29 1999</h3> |
| <ul> |
| <li>portability problems fixed</li> |
| <li>snprintf was used unconditionnally, leading to link problems on system |
| were it's not available, fixed</li> |
| </ul> |
| |
| <h3>1.7.1: Sep 24 1999</h3> |
| <ul> |
| <li>The basic type for strings manipulated by libxml has been renamed in |
| 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason |
| is that CHAR was conflicting with a predefined type on Windows. However on |
| non WIN32 environment, compatibility is provided by the way of a |
| <strong>#define </strong>.</li> |
| <li>Changed another error : the use of a structure field called errno, and |
| leading to troubles on platforms where it's a macro</li> |
| </ul> |
| |
| <h3>1.7.0: sep 23 1999</h3> |
| <ul> |
| <li>Added the ability to fetch remote DTD or parsed entities, see the <a |
| href="gnome-xml-nanohttp.html">nanohttp</a> module.</li> |
| <li>Added an errno to report errors by another mean than a simple printf |
| like callback</li> |
| <li>Finished ID/IDREF support and checking when validation</li> |
| <li>Serious memory leaks fixed (there is now a <a |
| href="gnome-xml-xmlmemory.html">memory wrapper</a> module)</li> |
| <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a> |
| implementation</li> |
| <li>Added an HTML parser front-end</li> |
| </ul> |
| |
| <h2><a name="XML">XML</a></h2> |
| |
| <p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for markup |
| based structured documents, here is <a name="example">an example</a>:</p> |
| <pre><?xml version="1.0"?> |
| <EXAMPLE prop1="gnome is great" prop2="&amp; linux too"> |
| <head> |
| <title>Welcome to Gnome</title> |
| </head> |
| <chapter> |
| <title>The Linux adventure</title> |
| <p>bla bla bla ...</p> |
| <image href="linus.gif"/> |
| <p>...</p> |
| </chapter> |
| </EXAMPLE></pre> |
| |
| <p>The first line specify that it's an XML document and gives useful |
| informations about it's encoding. Then the document is a text format whose |
| structure is specified by tags between brackets. <strong>Each tag opened have |
| to be closed</strong> XML is pedantic about this, not that for example the |
| image tag has no content (just an attribute) and is closed by ending up the |
| tag with <code>/></code>.</p> |
| |
| <p>XML can be applied sucessfully to a wide range or usage from long term |
| structured document maintenance where it follows the steps of SGML to simple |
| data encoding mechanism like configuration file format (glade), spreadsheets |
| (gnumeric), or even shorter lived document like in WebDAV where it is used to |
| encode remote call between a client and a server.</p> |
| |
| <h2><a name="tree">The tree output</a></h2> |
| |
| <p>The parser returns a tree built during the document analysis. The value |
| returned is an <strong>xmlDocPtr</strong> (i.e. a pointer to an |
| <strong>xmlDoc</strong> structure). This structure contains informations like |
| the file name, the document type, and a <strong>root</strong> pointer which |
| is the root of the document (or more exactly the first child under the root |
| which is the document). The tree is made of <strong>xmlNode</strong>s, chained |
| in double linked lists of siblings and with childs<->parent relationship. |
| An xmlNode can also carry properties (a chain of xmlAttr structures). An |
| attribute may have a value which is a list of TEXT or ENTITY_REF nodes.</p> |
| |
| <p>Here is an example (erroneous w.r.t. the XML spec since there should be |
| only one ELEMENT under the root):</p> |
| |
| <p><img src="structure.gif" alt=" structure.gif "></p> |
| |
| <p>In the source package there is a small program (not installed by default) |
| called <strong>tester</strong> which parses XML files given as argument and |
| prints them back as parsed, this is useful to detect errors both in XML code |
| and in the XML parser itself. It has an option <strong>--debug</strong> which |
| prints the actual in-memory structure of the document, here is the result with |
| the <a href="#example">example</a> given before:</p> |
| <pre>DOCUMENT |
| version=1.0 |
| standalone=true |
| ELEMENT EXAMPLE |
| ATTRIBUTE prop1 |
| TEXT |
| content=gnome is great |
| ATTRIBUTE prop2 |
| ENTITY_REF |
| TEXT |
| content= linux too |
| ELEMENT title |
| TEXT |
| content=Welcome to Gnome |
| ELEMENT chapter |
| ELEMENT title |
| TEXT |
| content=The Linux adventure |
| ELEMENT p |
| TEXT |
| content=bla bla bla ... |
| ELEMENT image |
| ATTRIBUTE href |
| TEXT |
| content=linus.gif |
| ELEMENT p |
| TEXT |
| content=...</pre> |
| |
| <p>This should be useful to learn the internal representation model.</p> |
| |
| <h2><a name="interface">The SAX interface</a></h2> |
| |
| <p>Sometimes the DOM tree output is just to large to fit reasonably into |
| memory. In that case and if you don't expect to save back the XML document |
| loaded using libxml, it's better to use the SAX interface of libxml. SAX is a |
| <strong>callback based interface</strong> to the parser. Before parsing, the |
| application layer register a customized set of callbacks which will be called |
| by the library as it progresses through the XML input.</p> |
| |
| <p>To get a more detailed step-by-step guidance on using the SAX interface of |
| libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> made <a |
| href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice |
| documentation.</a></p> |
| |
| <p>You can debug the SAX behaviour by using the <strong>testSAX</strong> |
| program located in the gnome-xml module (it's usually not shipped in the |
| binary packages of libxml, but you can also find it in the tar source |
| distribution). Here is the sequence of callback that would be generated when |
| parsing the example given before as reported by testSAX:</p> |
| <pre>SAX.setDocumentLocator() |
| SAX.startDocument() |
| SAX.getEntity(amp) |
| SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp; linux too') |
| SAX.characters( , 3) |
| SAX.startElement(head) |
| SAX.characters( , 4) |
| SAX.startElement(title) |
| SAX.characters(Welcome to Gnome, 16) |
| SAX.endElement(title) |
| SAX.characters( , 3) |
| SAX.endElement(head) |
| SAX.characters( , 3) |
| SAX.startElement(chapter) |
| SAX.characters( , 4) |
| SAX.startElement(title) |
| SAX.characters(The Linux adventure, 19) |
| SAX.endElement(title) |
| SAX.characters( , 4) |
| SAX.startElement(p) |
| SAX.characters(bla bla bla ..., 15) |
| SAX.endElement(p) |
| SAX.characters( , 4) |
| SAX.startElement(image, href='linus.gif') |
| SAX.endElement(image) |
| SAX.characters( , 4) |
| SAX.startElement(p) |
| SAX.characters(..., 3) |
| SAX.endElement(p) |
| SAX.characters( , 3) |
| SAX.endElement(chapter) |
| SAX.characters( , 1) |
| SAX.endElement(EXAMPLE) |
| SAX.endDocument()</pre> |
| |
| <p>Most of the other functionnalities of libxml are based on the DOM tree |
| building facility, so nearly everything up to the end of this document |
| presuppose the use of the standard DOM tree build. Note that the DOM tree |
| itself is built by a set of registered default callbacks, without internal |
| specific interface.</p> |
| |
| <h2><a name="library">The XML library interfaces</a></h2> |
| |
| <p>This section is directly intended to help programmers getting bootstrapped |
| using the XML library from the C language. It doesn't intent to be extensive, |
| I hope the automatically generated docs will provide the completeness |
| required, but as a separated set of documents. The interfaces of the XML |
| library are by principle low level, there is nearly zero abstration. Those |
| interested in a higher level API should <a href="#DOM">look at DOM</a>.</p> |
| |
| <p>The <a href="gnome-xml-parser.html">parser interfaces for XML</a> are |
| separated from the <a href="gnome-xml-htmlparser.html">HTML parser ones</a>, |
| let's have a look at how it can be called:</p> |
| |
| <h3><a name="Invoking">Invoking the parser : the pull way</a></h3> |
| |
| <p>Usually, the first thing to do is to read an XML input, the parser accepts |
| to parse both memory mapped documents or direct files. The functions are |
| defined in "parser.h":</p> |
| <dl> |
| <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> |
| <dd><p>parse a zero terminated string containing the document</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> |
| <dd><p>parse an XML document contained in a file (possibly compressed)</p> |
| </dd> |
| </dl> |
| |
| <p>This returns a pointer to the document structure (or NULL in case of |
| failure).</p> |
| |
| <h3 id="Invoking1">Invoking the parser: the push way</h3> |
| |
| <p>In order for the application to keep the control when the document is been |
| fetched (common for GUI based programs) the libxml, as of version 1.8.3 |
| provides a push interface too, here are the interfaces:</p> |
| <pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, |
| void *user_data, |
| const char *chunk, |
| int size, |
| const char *filename); |
| int xmlParseChunk (xmlParserCtxtPtr ctxt, |
| const char *chunk, |
| int size, |
| int terminate);</pre> |
| |
| <p>and here is a simple use example:</p> |
| <pre> FILE *f; |
| |
| f = fopen(filename, "r"); |
| if (f != NULL) { |
| int res, size = 1024; |
| char chars[1024]; |
| xmlParserCtxtPtr ctxt; |
| |
| res = fread(chars, 1, 4, f); |
| if (res > 0) { |
| ctxt = xmlCreatePushParserCtxt(NULL, NULL, |
| chars, res, filename); |
| while ((res = fread(chars, 1, size, f)) > 0) { |
| xmlParseChunk(ctxt, chars, res, 0); |
| } |
| xmlParseChunk(ctxt, chars, 0, 1); |
| doc = ctxt->myDoc; |
| xmlFreeParserCtxt(ctxt); |
| } |
| }</pre> |
| |
| <p>Also note that the HTML parser embedded into libxml also have a push |
| interface they are just prefixed by "html" instead of "xml"</p> |
| |
| <h3 id="Invoking2">Invoking the parser: the SAX interface</h3> |
| |
| <p>A couple of comments can be made, first this mean that the parser is |
| memory-hungry, first to load the document in memory, second to build the tree. |
| Reading a document without building the tree is possible using the SAX |
| interfaces (see SAX.h and <a |
| href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James |
| Henstridge documentation</a>), not also that the push interface can be limited |
| to SAX, just use the two first arguments of |
| <code>xmlCreatePushParserCtxt()</code>.</p> |
| |
| <h3><a name="Building">Building a tree from scratch</a></h3> |
| |
| <p>The other way to get an XML tree in memory is by building it. Basically |
| there is a set of functions dedicated to building new elements, those are also |
| described in "tree.h", here is for example the piece of code producing the |
| example used before:</p> |
| <pre> xmlDocPtr doc; |
| xmlNodePtr tree, subtree; |
| |
| doc = xmlNewDoc("1.0"); |
| doc->root = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); |
| xmlSetProp(doc->root, "prop1", "gnome is great"); |
| xmlSetProp(doc->root, "prop2", "& linux too"); |
| tree = xmlNewChild(doc->root, NULL, "head", NULL); |
| subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); |
| tree = xmlNewChild(doc->root, NULL, "chapter", NULL); |
| subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); |
| subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); |
| subtree = xmlNewChild(tree, NULL, "image", NULL); |
| xmlSetProp(subtree, "href", "linus.gif");</pre> |
| |
| <p>Not really rocket science ...</p> |
| |
| <h3><a name="Traversing">Traversing the tree</a></h3> |
| |
| <p>Basically by <a href="gnome-xml-tree.html">including "tree.h"</a> your code |
| has access to the internal structure of all the element of the tree. The names |
| should be somewhat simple like <strong>parent</strong>, |
| <strong>childs</strong>, <strong>next</strong>, <strong>prev</strong>, |
| <strong>properties</strong>, etc... For example still with the previous |
| example:</p> |
| <pre><code>doc->root->childs->childs</code></pre> |
| |
| <p>points to the title element,</p> |
| <pre>doc->root->childs->next->child->child</pre> |
| |
| <p>points to the text node containing the chapter titlle "The Linux adventure" |
| and</p> |
| |
| <p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be |
| present before the document root, so doc->root may point to an element which |
| is not the document Root Element, a function |
| <code>xmlDocGetRootElement()</code> was added for this purpose.</p> |
| |
| <h3><a name="Modifying">Modifying the tree</a></h3> |
| |
| <p>functions are provided to read and write the document content, here is an |
| excerpt from the <a href="gnome-xml-tree.html">tree API</a>:</p> |
| <dl> |
| <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const |
| xmlChar *value);</code></dt> |
| <dd><p>This set (or change) an attribute carried by an ELEMENT node the |
| value can be NULL</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar |
| *name);</code></dt> |
| <dd><p>This function returns a pointer to the property content, note that |
| no extra copy is made</p> |
| </dd> |
| </dl> |
| |
| <p>Two functions must be used to read an write the text associated to |
| elements:</p> |
| <dl> |
| <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar |
| *value);</code></dt> |
| <dd><p>This function takes an "external" string and convert it to one text |
| node or possibly to a list of entity and text nodes. All non-predefined |
| entity references like &Gnome; will be stored internally as an |
| entity node, hence the result of the function may not be a single |
| node.</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int |
| inLine);</code></dt> |
| <dd><p>this is the dual function, which generate a new string containing |
| the content of the text and entity nodes. Note the extra argument |
| inLine, if set to 1 instead of returning the &Gnome; XML encoding in |
| the string it will substitute it with it's value say "GNU Network Object |
| Model Environment". Set it if you want to use the string for non XML |
| usage like User Interface.</p> |
| </dd> |
| </dl> |
| |
| <h3><a name="Saving">Saving a tree</a></h3> |
| |
| <p>Basically 3 options are possible:</p> |
| <dl> |
| <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int |
| *size);</code></dt> |
| <dd><p>returns a buffer where the document has been saved</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> |
| <dd><p>dumps a buffer to an open file descriptor</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> |
| <dd><p>save the document ot a file. In that case the compression interface |
| is triggered if turned on</p> |
| </dd> |
| </dl> |
| |
| <h3><a name="Compressio">Compression</a></h3> |
| |
| <p>The library handle transparently compression when doing file based |
| accesses, the level of compression on saves can be tuned either globally or |
| individually for one file:</p> |
| <dl> |
| <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> |
| <dd><p>Get the document compression ratio (0-9)</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> |
| <dd><p>Set the document compression ratio</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>int xmlGetCompressMode(void);</code></dt> |
| <dd><p>Get the default compression ratio</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt><code>void xmlSetCompressMode(int mode);</code></dt> |
| <dd><p>set the default compression ratio</p> |
| </dd> |
| </dl> |
| |
| <h2><a name="Entities">Entities or no entities</a></h2> |
| |
| <p>Entities principle is similar to simple C macros. They define an |
| abbreviation for a given string that you can reuse many time through the |
| content of your document. They are especially useful when frequent occurrences |
| of a given string may occur within a document or to confine the change needed |
| to a document to a restricted area in the internal subset of the document (at |
| the beginning). Example:</p> |
| <pre>1 <?xml version="1.0"?> |
| 2 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [ |
| 3 <!ENTITY xml "Extensible Markup Language"> |
| 4 ]> |
| 5 <EXAMPLE> |
| 6 &xml; |
| 7 </EXAMPLE></pre> |
| |
| <p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing |
| it's name with '&' and following it by ';' without any spaces added. There |
| are 5 predefined entities in libxml allowing to escape charaters with |
| predefined meaning in some parts of the xml document content: |
| <strong>&lt;</strong> for the letter '<', <strong>&gt;</strong> for |
| the letter '>', <strong>&apos;</strong> for the letter ''', |
| <strong>&quot;</strong> for the letter '"', and <strong>&amp;</strong> |
| for the letter '&'.</p> |
| |
| <p>One of the problems related to entities is that you may want the parser to |
| substitute entities content to see the replacement text in your application, |
| or you may prefer keeping entities references as such in the content to be |
| able to save the document back without loosing this usually precious |
| information (if the user went through the pain of explicitley defining |
| entities, he may have a a rather negative attitude if you blindly susbtitute |
| them as saving time). The function <a |
| href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a> |
| allows to check and change the behaviour, which is to not substitute entities |
| by default.</p> |
| |
| <p>Here is the DOM tree built by libxml for the previous document in the |
| default case:</p> |
| <pre>/gnome/src/gnome-xml -> ./tester --debug test/ent1 |
| DOCUMENT |
| version=1.0 |
| ELEMENT EXAMPLE |
| TEXT |
| content= |
| ENTITY_REF |
| INTERNAL_GENERAL_ENTITY xml |
| content=Extensible Markup Language |
| TEXT |
| content=</pre> |
| |
| <p>And here is the result when substituting entities:</p> |
| <pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1 |
| DOCUMENT |
| version=1.0 |
| ELEMENT EXAMPLE |
| TEXT |
| content= Extensible Markup Language</pre> |
| |
| <p>So entities or no entities ? Basically it depends on your use case, I |
| suggest to keep the non-substituting default behaviour and avoid using |
| entities in your XML document or data if you are not willing to handle the |
| entity references elements in the DOM tree.</p> |
| |
| <p>Note that at save time libxml enforce the conversion of the predefined |
| entities where necessary to prevent well-formedness problems, and will also |
| transparently replace those with chars (i.e. will not generate entity |
| reference elements in the DOM tree nor call the reference() SAX callback when |
| finding them in the input).</p> |
| |
| <h2><a name="Namespaces">Namespaces</a></h2> |
| |
| <p>The libxml library implement namespace @@ support by recognizing namespace |
| contructs in the input, and does namespace lookup automatically when building |
| the DOM tree. A namespace declaration is associated with an in-memory |
| structure and all elements or attributes within that namespace point to it. |
| Hence testing the namespace is a simple and fast equality operation at the |
| user level.</p> |
| |
| <p>I suggest it that people using libxml use a namespace, and declare it on |
| the root element of their document as the default namespace. Then they dont |
| need to happend the prefix in the content but we will have a basis for future |
| semantic refinement and merging of data from different sources. This doesn't |
| augment significantly the size of the XML output, but significantly increase |
| it's value in the long-term.</p> |
| |
| <p>Concerning the namespace value, this has to be an URL, but this doesn't |
| have to point to any existing resource on the Web. I suggest using an URL |
| within a domain you control, which makes sense and if possible holding some |
| kind of versionning informations. For example |
| <code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme. |
| Then when you load a file, make sure that a namespace carrying the |
| version-independant prefix is installed on the root element of your document, |
| and if the version information don't match something you know, warn the user |
| and be liberal in what you accept as the input. Also do *not* try to base |
| namespace checking on the prefix value <foo:text> may be exactly the same |
| as <bar:text> in another document, what really matter is the URI |
| associated with the element or the attribute, not the prefix string which is |
| just a shortcut for the full URI.</p> |
| |
| <p>@@Interfaces@@</p> |
| |
| <p>@@Examples@@</p> |
| |
| <p>Usually people object using namespace in the case of validation, I object |
| this and will make sure that using namespaces won't break validity checking, |
| so even is you plan or are using validation I strongly suggest to add |
| namespaces to your document. A default namespace scheme |
| <code>xmlns="http://...."</code> should not break validity even on less |
| flexible parsers. Now using namespace to mix and differenciate content coming |
| from mutliple Dtd will certainly break current validation schemes, I will try |
| to provide ways to do this, but this may not be portable or standardized.</p> |
| |
| <h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2> |
| |
| <p>Well what is validation and what is a DTD ?</p> |
| |
| <p>Validation is the process of checking a document against a set of |
| construction rules, a <strong>DTD</strong> (Document Type Definition) is such |
| a set of rules.</p> |
| |
| <p>The validation process and building DTDs are the two most difficult parts |
| of XML life cycle. Briefly a DTD defines all the possibles element to be |
| found within your document, what is the formal shape of your document tree (by |
| defining the allowed content of an element, either text, a regular expression |
| for the allowed list of children, or mixed content i.e. both text and childs). |
| The DTD also defines the allowed attributes for all elements and the types of |
| the attributes. For more detailed informations, I suggest to read the related |
| parts of the XML specification, the examples found under |
| gnome-xml/test/valid/dtd and the large amount of books available on XML. The |
| dia example in gnome-xml/test/valid should be both simple and complete enough |
| to allow you to build your own.</p> |
| |
| <p>A word of warning, building a good DTD which will fit your needs of your |
| application in the long-term is far from trivial, however the extra level of |
| quality it can insure is well worth the price for some sets of applications or |
| if you already have already a DTD defined for your application field.</p> |
| |
| <p>The validation is not completely finished but in a (very IMHO) usable |
| state. Until a real validation interface is defined the way to do it is to |
| define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external |
| variable to 1, this will of course be changed at some point:</p> |
| |
| <p>extern int xmlDoValidityCheckingDefaultValue;</p> |
| |
| <p>...</p> |
| |
| <p>xmlDoValidityCheckingDefaultValue = 1;</p> |
| |
| <p></p> |
| |
| <p>To handle external entities, use the function |
| <strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to |
| link in you HTTP/FTP/Entities database library to the standard libxml |
| core.</p> |
| |
| <p>@@interfaces@@</p> |
| |
| <h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2> |
| |
| <p><a href="http://www.w3.org/DOM/">DOM</a> stands for the <em>Document Object |
| Model</em> this is an API for accessing XML or HTML structured documents. |
| Native support for DOM in Gnome is on the way (module gnome-dom), and it will |
| be based on gnome-xml. This will be a far cleaner interface to manipulate XML |
| files within Gnome since it won't expose the internal structure. DOM defines a |
| set of IDL (or Java) interfaces allowing to traverse and manipulate a |
| document. The DOM library will allow accessing and modifying "live" documents |
| presents on other programs like this:</p> |
| |
| <p><img src="DOM.gif" alt=" DOM.gif "></p> |
| |
| <p>This should help greatly doing things like modifying a gnumeric spreadsheet |
| embedded in a GWP document for example.</p> |
| |
| <p>The current DOM implementation on top of libxml is the <a |
| href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module</a>, this is |
| a full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph |
| Levien</a>.</p> |
| |
| <p>The gnome-dom module in the Gnome CVS base is obsolete</p> |
| |
| <h2><a name="Example"></a><a name="real">A real example</a></h2> |
| |
| <p>Here is a real size example, where the actual content of the application |
| data is not kept in the DOM tree but uses internal structures. It is based on |
| a proposal to keep a database of jobs related to Gnome, with an XML based |
| storage structure. Here is an <a href="gjobs.xml">XML encoded jobs |
| base</a>:</p> |
| <pre><?xml version="1.0"?> |
| <gjob:Helping xmlns:gjob="http://www.gnome.org/some-location"> |
| <gjob:Jobs> |
| |
| <gjob:Job> |
| <gjob:Project ID="3"/> |
| <gjob:Application>GBackup</gjob:Application> |
| <gjob:Category>Development</gjob:Category> |
| |
| <gjob:Update> |
| <gjob:Status>Open</gjob:Status> |
| <gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified> |
| <gjob:Salary>USD 0.00</gjob:Salary> |
| </gjob:Update> |
| |
| <gjob:Developers> |
| <gjob:Developer> |
| </gjob:Developer> |
| </gjob:Developers> |
| |
| <gjob:Contact> |
| <gjob:Person>Nathan Clemons</gjob:Person> |
| <gjob:Email>nathan@windsofstorm.net</gjob:Email> |
| <gjob:Company> |
| </gjob:Company> |
| <gjob:Organisation> |
| </gjob:Organisation> |
| <gjob:Webpage> |
| </gjob:Webpage> |
| <gjob:Snailmail> |
| </gjob:Snailmail> |
| <gjob:Phone> |
| </gjob:Phone> |
| </gjob:Contact> |
| |
| <gjob:Requirements> |
| The program should be released as free software, under the GPL. |
| </gjob:Requirements> |
| |
| <gjob:Skills> |
| </gjob:Skills> |
| |
| <gjob:Details> |
| A GNOME based system that will allow a superuser to configure |
| compressed and uncompressed files and/or file systems to be backed |
| up with a supported media in the system. This should be able to |
| perform via find commands generating a list of files that are passed |
| to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine |
| or via operations performed on the filesystem itself. Email |
| notification and GUI status display very important. |
| </gjob:Details> |
| |
| </gjob:Job> |
| |
| </gjob:Jobs> |
| </gjob:Helping></pre> |
| |
| <p>While loading the XML file into an internal DOM tree is a matter of calling |
| only a couple of functions, browsing the tree to gather the informations and |
| generate the internals structures is harder, and more error prone.</p> |
| |
| <p>The suggested principle is to be tolerant with respect to the input |
| structure. For example the ordering of the attributes is not significant, Cthe |
| XML specification is clear about it. It's also usually a good idea to not be |
| dependant of the orders of the childs of a given node, unless it really makes |
| things harder. Here is some code to parse the informations for a person:</p> |
| <pre>/* |
| * A person record |
| */ |
| typedef struct person { |
| char *name; |
| char *email; |
| char *company; |
| char *organisation; |
| char *smail; |
| char *webPage; |
| char *phone; |
| } person, *personPtr; |
| |
| /* |
| * And the code needed to parse it |
| */ |
| personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { |
| personPtr ret = NULL; |
| |
| DEBUG("parsePerson\n"); |
| /* |
| * allocate the struct |
| */ |
| ret = (personPtr) malloc(sizeof(person)); |
| if (ret == NULL) { |
| fprintf(stderr,"out of memory\n"); |
| return(NULL); |
| } |
| memset(ret, 0, sizeof(person)); |
| |
| /* We don't care what the top level element name is */ |
| cur = cur->childs; |
| while (cur != NULL) { |
| if ((!strcmp(cur->name, "Person")) && (cur->ns == ns)) |
| ret->name = xmlNodeListGetString(doc, cur->childs, 1); |
| if ((!strcmp(cur->name, "Email")) && (cur->ns == ns)) |
| ret->email = xmlNodeListGetString(doc, cur->childs, 1); |
| cur = cur->next; |
| } |
| |
| return(ret); |
| }</pre> |
| |
| <p>Here is a couple of things to notice:</p> |
| <ul> |
| <li>Usually a recursive parsing style is the more convenient one, XML data |
| being by nature subject to repetitive constructs and usualy exibit highly |
| stuctured patterns.</li> |
| <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e. |
| the pointer to the global XML document and the namespace reserved to the |
| application. Document wide information are needed for example to decode |
| entities and it's a good coding practice to define a namespace for your |
| application set of data and test that the element and attributes you're |
| analyzing actually pertains to your application space. This is done by a |
| simple equality test (cur->ns == ns).</li> |
| <li>To retrieve text and attributes value, it is suggested to use the |
| function <em>xmlNodeListGetString</em> to gather all the text and entity |
| reference nodes generated by the DOM output and produce an single text |
| string.</li> |
| </ul> |
| |
| <p>Here is another piece of code used to parse another level of the |
| structure:</p> |
| <pre>/* |
| * a Description for a Job |
| */ |
| typedef struct job { |
| char *projectID; |
| char *application; |
| char *category; |
| personPtr contact; |
| int nbDevelopers; |
| personPtr developers[100]; /* using dynamic alloc is left as an exercise */ |
| } job, *jobPtr; |
| |
| /* |
| * And the code needed to parse it |
| */ |
| jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { |
| jobPtr ret = NULL; |
| |
| DEBUG("parseJob\n"); |
| /* |
| * allocate the struct |
| */ |
| ret = (jobPtr) malloc(sizeof(job)); |
| if (ret == NULL) { |
| fprintf(stderr,"out of memory\n"); |
| return(NULL); |
| } |
| memset(ret, 0, sizeof(job)); |
| |
| /* We don't care what the top level element name is */ |
| cur = cur->childs; |
| while (cur != NULL) { |
| |
| if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) { |
| ret->projectID = xmlGetProp(cur, "ID"); |
| if (ret->projectID == NULL) { |
| fprintf(stderr, "Project has no ID\n"); |
| } |
| } |
| if ((!strcmp(cur->name, "Application")) && (cur->ns == ns)) |
| ret->application = xmlNodeListGetString(doc, cur->childs, 1); |
| if ((!strcmp(cur->name, "Category")) && (cur->ns == ns)) |
| ret->category = xmlNodeListGetString(doc, cur->childs, 1); |
| if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns)) |
| ret->contact = parsePerson(doc, ns, cur); |
| cur = cur->next; |
| } |
| |
| return(ret); |
| }</pre> |
| |
| <p>One can notice that once used to it, writing this kind of code is quite |
| simple, but boring. Ultimately, it could be possble to write stubbers taking |
| either C data structure definitions, a set of XML examples or an XML DTD and |
| produce the code needed to import and export the content between C data and |
| XML storage. This is left as an exercise to the reader :-)</p> |
| |
| <p>Feel free to use <a href="gjobread.c">the code for the full C parsing |
| example</a> as a template, it is also available with Makefile in the Gnome CVS |
| base under gnome-xml/example</p> |
| |
| <p></p> |
| |
| <p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p> |
| |
| <p>$Id: xml.html,v 1.23 2000/01/25 18:31:22 veillard Exp $</p> |
| </body> |
| </html> |