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Sometimes when I'm working with EER diagrams I see different symbols, for example, 'd', 'o', 'u' and so on. Like the 'd' here

What do they mean and what are they used for? And how many variants do it exists?

BlommaN
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1 Answers1

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1.d means "disjoint"- what it tells is the subclasses must have disjoint sets of entities.

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2.o means "overlap"The subclasses may have overlapping sets of entities. enter image description here

  1. U symbol indicates the Subtype is a subset of the Supertype. enter image description here

4.Place o or d in specialization circle to indicate constraint.

AVI
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