EntityRelationshipModeling by BernhardThalheim
ISBN: 3540654704 It's a consolidation of much of the research work that has gone on since Chen's introduction of the ER model. It's quite powerful, but most of the literature is rather formal and a bit difficult for non-logicians to parse (thus far).
More information:
- Book available at discount -- http://www.informatik.tu-cottbus.de/~thalheim/HERM.htm
- Postscript Downloads of accompanying material -- http://www.informatik.tu-cottbus.de/~thalheim/slides.htm
See also EntityRelationshipDiagram