Chapter Notes

By depicting each role as a box associated with a table column, Object-Role Modeling enables uniqueness constraints to be portrayed in a natural way where the impact of the constraint on populations is immediately apparent. Entity Relationship modeling (ER) and UML depict internal uniqueness constraints on associations using a variety of notations for “cardinality constraints” or “multiplicity constraints”, as discussed later. ER offers graphical support for some uniqueness constraints on attributes, but UML does not. Neither ER nor UML offers any significant support for external uniqueness constraints.

Object-Role Modeling makes minimal use of the notion of functional dependency, but this notion is central to many other methods. For a clear treatment of an ER approach as well as functional dependency theory, see Elmasri and Navathe (1994).

Although it is generally wise to objectify a predicate only if it has a spanning uniqueness constraint, rare cases may arise where it may be useful to remove this restriction, as discussed in Chapter 10.