The DOM Model Page 33

Under DOM, all XML documents have a root node. Each document must have one and only one root node. In our sample XML document, travel.xml, the root node is Recordset, and can be written in the XML document as <Recordset> ... </Recordset>. The nesting of the elements within an XML document is what defines the tree structure. The root node has one or more child nodes. Each child node can have one or more additional child nodes. Travelpackage is the child node of Recordset. Child nodes are nested inside their parent node.

The document tree for the XML document travel.xml is shown in this figure:

Using PHP's DOM Support

DOM is not a part of the standard PHP configuration. In order to use the DOM functions, you must configure PHP by specifying the --with-dom argument. You will need the libxml libraries before configuring PHP. For Linux and UNIX servers, you can download the library from: http://www.xmlsoft.org/. If you are running Windows, then there is a Windows port available: http://www.fh- frankfurt.de/~igor/projects/libxml/index.html.

Getting DOM to work with Windows and Apache is not a trivial task. If you are having problems getting the DOM code to work, then here are some things to check:

• Open php.ini. There's two things we're looking for, extension_dir and extension=php_domxml.dll. The first setting to look at is extension_dir. This defines where the files that provide the functionality for extensions to PHP, like DOM, are stored. About half way down the file you should see a section called Paths and Directories, and the extension_dir directive. Here, the value for extension_dir is "./", which means the current folder:

     ;;;;;;;;;;;;;;;;;;;;;;;;;
     ; Paths and Directories ;
     ;;;;;;;;;;;;;;;;;;;;;;;;;
  
     extension_dir    =    ./    ; directory in which the 
     loadable extensions (modules) reside
  

  Remember the setting for extension_dir. It doesn't really matter where the directory is, but you should make sure that the php_domxml.dll file is in there.

  A little further down is a section titled Windows Extensions. Look for the entry extension=php_domxml.dll. Make sure there isn't a semi-colon (;) in front of it. If there is, delete the semi-colon and then save and exit the php.ini file.

• Make sure libxml.dll and iconv.dll are in the C:\WINNT\System32\ directory.

PHP's DOM XML functions are still experimental (as of PHP 4.0.6). The actual usage of DOM within PHP may change when they've matured.

DOM Example Code

The DOM API enables very easy reading and writing of XML. We will use DOM to create an XML file, parse that same file, convert it to HTML, and display it as a table.

Writing XML with DOM

The first thing we have to do is to create the new DOM object. The string in the parenthesis becomes the version number for the XML declaration in the resulting XML file:

   <?php 
   $doc = new_xmldoc("1.0");

Then we have to define the root node:

$root = $doc->add_root("Recordset");

Now, let's add branches to the tree by using new_child(). This function has two parameters, the first one becomes the name of the node and the second one becomes the value. In this example, we want the child under Recordset to be Travelpackage, and it doesn't have any contents so we leave the string empty. If there isn't any data for the tag, we have to include the empty string. If the string is left empty, the XML file will not be well- formed:

$one = $root->new_child("Travelpackage", "");

SAX Example Code Page 32
Professional PHP4 Programming
The DOM Model Page 34