Effective XML: 50 Specific Ways to Improve Your XML

Item 37. Validate Inside Your Program with Schemas

Rigorously testing preconditions is an important characteristic of robust, reliable software. Schemas make it very easy to define the preconditions for XML documents you parse and the postconditions for XML documents you write. Even if the document itself does not have a schema, you can write one and use it to test the documents before you operate on them. It is quite hard to attach a DTD to a document inside a program. Fortunately, however, most other schema languages are much more flexible about this.

For example, let's suppose you're in charge of a system at TV Guide that accepts schedule information from individual stations over the Web. Information about each show arrives as an XML document ...