Ive heard that XML does not require a DTD. That makes XML very simple to implement, right?
Although the XML standard makes supplying a DTD optional, for most serious applications, we believe it is prudent to build a DTD to go along with your application. XML allows you to define your own document elements. Without a DTD, you can verify that a document is well-formed, but not which particular document elements you want to allow, and in what order. Having a DTD allows you to use XML tools (many of which are free and available in the public domain) to validate your documents. A validating processor can check for much more than just well-formedness. In particular, it can check the document structure against a set of declarations to make sure that the structure contains all the parts (and no extra parts) required by those declarations. This makes it easy to use XML to define a format, and then test documents against that format to make sure they meet all requirements laid out by the declarations. In DCL’s experience, documentation tends to vary greatly in consistency. While it is
