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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We are getting great response for the RealWorld DITA Conference here in Raleigh and have great speakers lined up -- including multiple speakers from IBM. 

Conference info is online at http://www.aboveandbeyondlearning.com/ditaconference.html

This article was written for those new to XML, and may be helpful to those new to XML and DITA... give you a foundation on which to build.

http://www.ibm.com/developerworks/xml/library/x-newxml/