PHP Cookbook

12.3. Parsing XML with the DOM

Problem

You want to parse an XML file using the DOM API. This puts the file into a tree, which you can process using DOM functions. With the DOM, it’s easy to search for and retrieve elements that fit a certain set of criteria.

Solution

Use PHP’s DOM XML extension. Here’s how to read XML from a file:

$dom = domxml_open_file('books.xml');

Here’s how to read XML from a variable:

$dom = domxml_open_mem($books);

You can also get just a single node. Here’s how to get the root node:

$root = $dom->document_element( );

Here’s how to do a depth-first recursion to process all the nodes in a document:

function process_node($node) {
    if ($node->has_child_nodes( )) {
        foreach($node->child_nodes( ) as $n) {
            process_node($n);
        }
    }

    // process leaves
    if ($node->node_type( ) =  = XML_TEXT_NODE) {
        $content = rtrim($node->node_value( ));
        if (!empty($content)) {
            print "$content\n";
        }
    }

}
process_node($root);

Discussion

The W3C’s DOM provides a platform- and language-neutral method that specifies the structure and content of a document. Using the DOM, you can read an XML document into a tree of nodes and then maneuver through the tree to locate information about a particular element or elements that match your criteria. This is called tree-based parsing . In contrast, the non-DOM XML functions allow you to do event-based parsing.

Additionally, you can modify the structure by creating, editing, and deleting nodes. In fact, you can use the DOM XML functions to author a new XML ...