Perl and XML

Chapter 7. DOM

In this chapter, we return to standard APIs with the Document Object Model (DOM). In Chapter 5, we talked about the benefits of using standard APIs: increased compatibility with other software components and (if implemented correctly) a guaranteed complete solution. The same concept applies in this chapter: what SAX does for event streams, DOM does for tree processing.

DOM and Perl

DOM is a recommendation by the World Wide Web Consortium (W3C). Designed to be a language-neutral interface to an in-memory representation of an XML document, versions of DOM are available in Java, ECMAscript,^[1] Perl, and other languages. Perl alone has several implementations of DOM, including XML::DOM and XML::LibXML.

While SAX defines an interface of handler methods, the DOM specification calls for a number of classes, each with an interface of methods that affect a particular type of XML markup. Thus, every object instance manages a portion of the document tree, providing accessor methods to add, remove, or modify nodes and data. These objects are typically created by a factory object, making it a little easier for programmers who only have to initialize the factory object themselves.

In DOM, every piece of XML (the element, text, comment, etc.) is a node represented by a Node object. The Node class is extended by more specific classes that represent the types of XML markup, including Element, Attr (attribute), ProcessingInstruction, Comment, EntityReference, Text, CDATASection,