Part IV
Identity
Identity is the property that distinguishes an entity from all others. Identity is a prominent concern in databases because developers must be able to find and reference data. This chapter focuses on conceptual aspects of identity and minimizes the discussion of implementation.
Identity is relevant to patterns, because identity deeply pervades models and thinking about models. There are three purposes of data models: to define data structure, to constrain data, and to provide a blueprint for accessing data. Identity is important for all three. Identifying fields are prominent in the declaration of data structure. Identity is by its very nature a constraint on uniqueness. And finally, unique fields and unique combinations of fields ...
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