Good readings about refactoring data structures

Nowadays most programmers know about c开发者_StackOverflow社区ode refactorings.

What about refactorings of data structures, are there any good readings about it?

One paradigm that I can think of is the normalization process of a relational database.

Are there any other good examples?

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Much like code, data can be refactored by using an abstraction layer in front of it. Instead of using raw SQL to access your data, put a layer in front of it to abstract the queries. Not only will it let you refactor the data structure but it'll also let you completely change your data repository.

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Refactoring Databases : Evolutionary Database Design seems to be a worthwile read on the subject, judging from the fact that it won the 2007 Software Development Jolt Productivity Award in the Technical Books category. I haven't yet read it though, so I can't comment on it personally.

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xUnit Test Patterns: Refactoring Test Code is a good reference for refactoring your code to work well with unit tests. It's not exactly what your asking for but its a good reference to keeep on hand.