PHP DOM & XPath

The Document Object Model (DOM) is a programming API for HTML and XML documents defining the logical structure.

XPath (XML Path Language) is based on a tree representation of the XML/HTML document, and provides the ability to navigate around the tree, selecting nodes by a variety of criteria.

Introduction

The Document Object Model or DOM in combination with XPath are powerful/useful tools for screen scraping, programming and data manipulation (and much more). Unfortunately all the features are less known, often poorly documented and with very little tutorials.

Also the DOM and XPath can be used in PHP and in Javascript or better on the server and in the client-browser.

Structuring XML and HTML

Node Relations

Node Relations

The nodes in the node tree have a hierarchical relationship to each other which have to be defined clearly:

• Root : the top node of the tree,
• Parent : every node has exactly one parent except the root, which has no parent,
• Child : A node can have a number of children,
• Sibling : Siblings (brothers or sisters) are nodes with the same parent.

From the HTML on the right you can read
html is the root node, html has no parents, html is the parent of head and body, head is the first child of html, body is the last child of html,	head has one child: title title has one child (a text node): "DOM Tutorial" body has two children: h1 and p h1 has one child: "DOM Lesson one" p has one child: "Hello world!" h1 and p are siblings
Use the following node properties to navigate between nodes
parentNode childNodes[nodenumber] firstChild lastChild nextSibling previousSibling