Semantic data models have emerged from a requirement for more expressive conceptual data models. Current generation data models lack direct support for relationships, data abstraction, inheritance, constraints, unstructured objects, and the dynamic properties of an application. Although the need for data models with richer semantics is widely recognized, no single approach has won general acceptance.

a. What are the generic properties of semantic data models?

b. Present a representative selection of models that have been proposed since the mid-1970s.

c. Offer guidelines for the comparison of models.

d. Discuss the future directions in the population of conceptual data modeling.