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XML is not Objects!

An XML document can be represented using objects, and this is precisely the approach taken by DOM and JDOM. An XML parser can be used to create an appropriate object representation of an XML document without involving the programmer. However, the fundamental types of XML are not fundamental in object oriented languages, so casting and conversion is frequently required. Similarly, the basic notions of hierarchy and containment are not directly supported in the object oriented model, so explicit navigation is often required. This causes significant work for the programmer.

Adam Bosworth pointed this out with the following example. Suppose a programmer wants to compute price/earnings ratios from an XML feed. An individual stock might be represented as follows:

To compute the price/earnings ratio, we use the formula "pe = price / (revenues - expenses)". To do this with the DOM, we also need to parse the XML, navigate to the places where this information is found, and convert the text of the document to the appropriate datatype. Here is the DOM code Adam provides for this:

This solution would have been much messier if Adam had not used the path expressions of XPath, a simple Native XML language. In XQuery, path expressions are part of the language, and numeric conversions are automatically done for untyped data. If the data is validated against a schema, the types assigned by the schema are used. This makes it possible to solve the same problem much more simply:

For XML-centric applications, an object-oriented representation of an XML document imposes unneeded overhead that complicates programs.