DITA Specialization opens a new dimension for customizing DITA to needs of different enterprises. But doing a valid specialization is not a trivial process. It requires rather deep understanding of DITA internals and command in technologies like DTD, XML Schema and s.o.

But even with sufficient knowledge of DTD (or XML Schema) coding, doing a valid specialization requires knowledge of certain DITA principles and rules. Just designing a valid DTD will not necessarily mean that you have a valid DITA model. 

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