Python & XML

Understanding the DOM

The DOM structure is essentially a hierarchy of node objects. Beginning with the root of the document (not the same as the document element), all constructs in the document are represented by nodes of various types, whether an element, text, attributes of elements, or other less common node types. Each node contains a list of references to child nodes, which can in turn be of the same types as those contained by the parent node. Therefore, a complete document looks just like a tree, all the way from the “trunk” (or root element of the tree) out to the leaf nodes representing text, childless elements, comments, processing instructions, and possibly other constructs. Figure 4-1 shows a very simple DOM hierarchy including a root element, two child elements, and their respective child text elements. Usually the character data of an element consists of multiple text nodes depending on the parser in use. Contiguous strings of textual data become sequences of text nodes.

Figure 4-1. A simple DOM hierarchy

When a document is represented by the DOM, an object hierarchy represents the entire document. As with other nodes, it can contain children; the outermost element of the document is simply a child of the document node. The document can have other children; comments and processing instructions can precede or succeed the document element and appear in the proper order ...