Design

The Oracle XML Parsers support the DOM (Document Object Model) and SAX (Simple API for XML) interfaces. This tutorial uses the SAX API to normalize an XML document. Here's why.

XML APIs generally fall into two categories: tree-based and event-based. A tree-based API (such as DOM) builds an in-memory tree representation of the XML document. It provides classes and methods for an application to navigate and process the tree. In general, the DOM interface is most useful for structural manipulations of the XML tree, such as reordering elements, adding or deleting elements and attributes, renaming elements, and so on.

An event-based API (such as SAX) uses callbacks to report parsing events to the application. The application deals with these events through customized event handlers. Events include the start and end of elements and characters. Event-based APIs usually do not build in-memory tree representations of the XML documents. Therefore, in general, SAX is useful for applications that do not need to manipulate the XML tree, such as search operations, among others.

The following figure shows an XML document and corresponding SAX and DOM representations.

XML Document	SAX Events	DOM Tree
<?xml version="1.0"?>   <EMPLIST>     <EMP>      <ENAME>MARTIN</ENAME>     </EMP>     <EMP>      <ENAME>SCOTT</ENAME>     </EMP>   </EMPLIST>	start document start element: EMPLIST start element: EMP start element: ENAME characters: MARTIN end element: EMP start element: EMP start element: ENAME characters: SCOTT end element: EMP  end element: EMPLIST end document

So, because normalization involves processing document elements to remove whitespace characters, this tutorial uses SAX instead of DOM.