Chapter Notes
Not all versions of ORM allow independent entity types. FCO-IM (Bakema et al., 1994) handles the problem by treating entity types as objectifications of unaries.
Most versions of ER do not allow subset, equality, or exclusion constraints between role-sequences, or attributes, to be included on the schema diagram (see Chapter 8). UML includes graphic symbols for subset constraints only between whole associations, and exclusion constraints only in the context of an exclusive-or constraint between roles (see Chapter 9). Recent versions of ER, as well as UML, offer basic support for subtyping, but ignore the need for formal subtype definitions or context-dependent reference (see Chapters8 and 9).
Some versions of ORM restrict subtypes ...
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