Rating: 
Summary: It delivers
Review: This book delivered on my expectations. I was being asked to build a ground-up billing and accounting system, and this book really helped bring clarity to my conceptions and design. This book should be studied.I've omitted a star because this is very much an applied data model pattern book. More esoteric modeling problems, such as meta-data representations of real or digitial world entities are not covered.
Rating: 
Summary: Not Practical
Review: This book provides you with patterns for creating conceptual data models. It's not practical, though, in that it does not provide insight into how to go from conceptual to real. In fact, it's almost useless. These "patterns" are nothing more than concepts that good data modelers instinctively know already. Also, his ER modeling techniques are a bit outdated. Finally, this book is very, very dense and difficult to read. He just describes how to set up the models in very dense language, without going into the why's. It becomes virtually unreadable after the second or third pattern. There are other, more recent books out there which provide better, more up to date thinking on this nascent topic (which I believe is still years, if not decades away from truly practical modeling/process techniques).
Rating:
Summary: Not Practical
Review: This book provides you with patterns for creating conceptual data models. It's not practical, though, in that it does not provide insight into how to go from conceptual to real. In fact, it's almost useless. These "patterns" are nothing more than concepts that good data modelers instinctively know already. Also, his ER modeling techniques are a bit outdated. Finally, this book is very, very dense and difficult to read. He just describes how to set up the models in very dense language, without going into the why's. It becomes virtually unreadable after the second or third pattern. There are other, more recent books out there which provide better, more up to date thinking on this nascent topic (which I believe is still years, if not decades away from truly practical modeling/process techniques).
Rating: 
Summary: Abstract but easy reading
Review: This book's high level of abstraction makes is great for generic models that you "massage" to form your own final design. In essence, all the serious fundamental errors can be obliterated by following Hay's designs, giving you a very robust base design. Probably, best of all, is the easy writing style; making the technical stuff a lot easier. If you want something that holds your hand a bit more, get "The Data Model Resource Book".
Rating:
Summary: Fantastic Collection of Ideas
Review: This books is great for getting ideas. I use it to help me think about data models that I'm creating. Hay presents his thinking from many perspectives. He's not trying to say, "Here's how you do this data model." What he does is present different aspects of modeling various subject areas; illustrating various slants at approaching models for the subject area. This is very helpful when brainstorming or trying to come up with a model. This book is a great reference that I consult consistently at the beginning of each new modeling task. A must have.
Rating:
Summary: Clear conceptual data models for recurring business problems
Review: This excellent book follows the methods of Richard Barker (CASE Method Entity Relationship Modeling, Addison Wesley Publishing Company, 1990) to examine numerous patterns in conceptual data structures which occur frequently throughout business, industry, and government. The included examples will solve many modeling problems for every organization and skip over the "reinvent the wheel" stage of many projects.
Rating:
Summary: Data Modeling Nirvana
Review: Tour de force! This book is up there with Gamma et al's "Design Patterns" and Booch's "Object-Oriented Design" for helping me to achieve a breakthrough understanding of--in this case--database-oriented data models. Hays walks the reader through all the important domains of business--people, assets, accounting, contracts, document management, projects--and builds a concrete data model of each domain. As he proceeds through each model he draws comparisons to the previous ones revealing patterns common to all the domains. In the last chapter he summarizes the patterns and build a universal data model that applies to all domains. I believe this book can be very helpful in the development of data models in any field for two reasons. One, you can view the domain you are dealing with as a variation on one or more of the domains he presents and apply elements to your situation. Two, you can view your domain under the more abstract concepts that cut across all the domains. It's the combination and synthesis of both these elements that makes the book powerful and led me to a few moments of data modeling nivrana. This book won't help you to make tough physical database design decisions, but it may be indispensable to understanding the prerequisite analysis.
Rating:
Summary: Data Modeling Nirvana
Review: Tour de force! This book is up there with Gamma et al's "Design Patterns" and Booch's "Object-Oriented Design" for helping me to achieve a breakthrough understanding of--in this case--database-oriented data models. Hays walks the reader through all the important domains of business--people, assets, accounting, contracts, document management, projects--and builds a concrete data model of each domain. As he proceeds through each model he draws comparisons to the previous ones revealing patterns common to all the domains. In the last chapter he summarizes the patterns and build a universal data model that applies to all domains. I believe this book can be very helpful in the development of data models in any field for two reasons. One, you can view the domain you are dealing with as a variation on one or more of the domains he presents and apply elements to your situation. Two, you can view your domain under the more abstract concepts that cut across all the domains. It's the combination and synthesis of both these elements that makes the book powerful and led me to a few moments of data modeling nivrana. This book won't help you to make tough physical database design decisions, but it may be indispensable to understanding the prerequisite analysis.
Rating:
Summary: Data Modeling Nirvana
Review: Tour de force! This book is up there with Gamma et al's "Design Patterns" and Booch's "Object-Oriented Design" for helping me to achieve a breakthrough understanding of--in this case--database-oriented data models. Hays walks the reader through all the important domains of business--people, assets, accounting, contracts, document management, projects--and builds a concrete data model of each domain. As he proceeds through each model he draws comparisons to the previous ones revealing patterns common to all the domains. In the last chapter he summarizes the patterns and build a universal data model that applies to all domains. I believe this book can be very helpful in the development of data models in any field for two reasons. One, you can view the domain you are dealing with as a variation on one or more of the domains he presents and apply elements to your situation. Two, you can view your domain under the more abstract concepts that cut across all the domains. It's the combination and synthesis of both these elements that makes the book powerful and led me to a few moments of data modeling nivrana. This book won't help you to make tough physical database design decisions, but it may be indispensable to understanding the prerequisite analysis.
Rating: 
Summary: Relational modeling and not object modeling
Review: With heavy emphasis in the manufacturing and supply-chain world, this book provides a treasure-chest of reusable concepts and data modeling frameworks on which to grow to model a business. Strongly slanted towards relational database modeling, it has a totally different flavor than from a book slanted towards object modeling, such as Analsys Patterns by Martin Fowler. A cheaper version of this book, and in my view just as good is The Data Model Resource Book by Len Silverston. It would be nice to see this book into a second edition with XML templates representing invoices, customers, contacts, billing item, etc etc.
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