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Common Warehouse Metamodel: An Introduction to the Standard for Data Warehouse Integration Review by David C. Hay
The emperor has no clothes
Ok, I am a known heretic. I am not impressed by the CWM model. It is oriented toward the object-oriented implementation of a tool for metadata exchange, not toward representing the things business people would be looking for in a meta data repository.
This book is better than the on-line specification at describing the model--which was really incomprehensible--but this is at the expense of completeness. Definitions are not available for all classes and the ones that are are not clear (to me at least). The relationships are barely defined at all.
In fairness, the model is so complex that it may not be possible to describe clearly to anyone not deeply immersed in the language of object-orientation. The team of authors is further hampered by its use of UML. The notation does not permit a complete inheritance tree to be portrayed in a diagram if the diagram is of less than the entire model. Two classes may be related, but you can't see this because the relationship is between great grandparents, shown on a different page.