Information Modeling and Relational Databases, 2nd Edition

Chapter Notes

Some versions of ORM use a universal quantifier () instead of the mandatory role dot, and place this along the role connector instead of at one end (e.g., DeTroyer et al. 1988). As discussed in later chapters, ER and UML support simple mandatory role constraints for most situations, but not disjunctive mandatory role constraints. Some versions of ER use a solid line for mandatory and a broken one for optional (e.g., Barker 1990), some use double lines for mandatory (e.g. Elmasri and Navathe 1994), and some, including UML, use cardinality or multiplicity markers such as 0 for optional and 1 (or more) for mandatory. UML allows attributes ...