EER Diagrams, different symbols?

database database-design diagram eer-model
BlommaN picture BlommaN · Oct 14, 2015 · Viewed 8.3k times · Source

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?

Answer

AVI picture AVI · Nov 25, 2015

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.

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