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In data modeling, what is the preference on discriminator in the generalization process?

Published
  • May 07 2004, 1:00am EDT
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Q:  

In data modeling, what is the preference on discriminator in the generalization process? Is it necessary to have a "type" attribute in super-type entity?

A:  

Les Barbusinski's Answer: I've never seen a data modeling tool that doesn't require a TYPE attribute to discriminate entity "sub-types" within a "super-type" ... so that sort of dictates your answer. In the real world, entity sub-types can be distinguished in one of three ways:

  • By the value of a single attribute (i.e., a TYPE)
  • Groups of values in a single attribute (e.g. a value of "A", "B", or "C" indicates entity sub-type 1, while all other values indicate entity sub-type 2)
  • Correlated values across several attributes (e.g., an "A" in attribute X and a "12" in attribute Y indicates entity sub-type 1, while all other combinations indicate entity sub-type 2)

However, as a practical matter, all of these discriminators need to be "distilled" down to a single TYPE attribute in a data model. Hope this helps.

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