Here's how I spent part of my morning in an empty house.
He'll need it.QuestionDec 05, 2009Sent to Aardvark via IMFriend 122 / M / Omaha, NEIn database design, are relational schemas created with ER diagrams usually in 3NF? Is there a case where ERD schemas wouldn't be in 3NF?
Answer 1+ 11 minutesAardvark found someone who knows about database
William A. (<--- that's me)I am a database architect. For a relational system, yes, diagrams are created with at least third normal form. It is a part of the design process to consider business rules, usage and business entities... strictly designing a system to a normalization spec is not realistic. When designing a data warehouse however, converting higher-normalization relational data into a less normalized form may lead to better performance in a system that will be primarily for reads, not writes.
Friend 1Is there a something about the ERD approach to designing relational schemas that makes it generally create schemas that satisfy third normal form, or is it just something you keep in mind during the design process?
William A.So, I wasn't aware ERD was an "approach". Typically a CERD is followed by a PERD. That is, a Conceptual ERD, where relationships are specified as M-M, and objects are in business terms that a client would be able to easily recognize and comprehend. A Physical ERD is not easily consumable by a client or business user because it translates the CERD into database tables and foreign key relationships. The PERD contains join tables that break many to many relationships into a pair of 1-M relationships, for example. So building an ERD is to me separate from proper Normalization methodology.
Friend 1Yeah, ERD schema design and 3NF normalization are usually not thought of simultaneously, which is why I'm having a hard time finding any resources that relate the two. Much harder is figuring out how well ERD creates schemas which satisfy 3NF, whether that was the intention of the design or not.
William A.To me, ERD is not a design process or architecture methodology. To me, it is a document. Yes, ERD can display a schema that has been created in 3NF well, though typically only a PERD would be capable to displaying proper normalization. I'd suggest papers or books by CJ Date or EF Codd
Friend 1I'll look into it, thanks for your help.
William A.good luck
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