EER Diagrams, different symbols?

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?


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

2.o means "overlap"The subclasses may have overlapping sets of entities.

  1. U symbol indicates the Subtype is a subset of the Supertype.

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

Same time i found great link about EER diagrams, just refer it if you want.-

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