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| <h1 align="center">The XML library for Gnome</h1> |
| <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. The internal document |
| repesentation is as close as possible to the <a |
| href="http://www.w3.org/DOM/">DOM</a> interfaces.</p> |
| |
| <h2>xml</h2> |
| <p> |
| XML is a standard 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="&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 |
| tage has no content (just an attribute) and is closed by ending up the tag |
| with <code>/></code>.</p> |
| |
| <h2>The tree output</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= too |
| ELEMENT head |
| ELEMENT title |
| content=Welcome to Gnome |
| ELEMENT chapter |
| ELEMENT title |
| content=The Linux adventure |
| ELEMENT p |
| content=bla bla bla ... |
| ELEMENT image |
| ATTRIBUTE href |
| TEXT |
| content=linus.gif |
| ELEMENT p |
| content=...</pre> |
| <p> |
| This should be useful to learn the internal representation model.</p> |
| |
| <h2>The XML library interfaces</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> |
| (unfortunately not completed).</p> |
| |
| <h3>Invoking the parser</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>xmlDocPtr xmlParseMemory(char *buffer, int size);</dt> |
| <dd><p> |
| parse a zero terminated string containing the document</p> |
| </dd> |
| </dl> |
| <dl> |
| <dt>xmlDocPtr xmlParseFile(const char *filename);</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> |
| <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 will be possible in the future by |
| pluggin the code to the SAX interface (see SAX.c).</p> |
| |
| <h3>Traversing the tree</h3> |
| <p> |
| Basically by including "tree.h" 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... </p> |
| |
| <h3>Modifying the tree</h3> |
| |
| <h3>Saving a tree</h3> |
| |
| <h2><a name="DOM">DOM interfaces</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. DOM defiles 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> |
| </p> |
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