Ternary Relationships: Semantic Requirements and Logically Correct Alternatives

Abstract

Conceptual data modeling is a backbone of most major systems development projects. Within this arena, one of the most widely used techniques is the entity-relationship (ER) or extended entity-relationship model (EER, henceforth also referred to as ER), introduced by Chen (1976). However, there are multiple competing models and notations, each having distinct strengths and weaknesses. Many of the model definitions and underpinnings continue to undergo practical and theoretical development. The abilities of each of the model structures and notations to fully represent the semantics of any given situation are constantly compared, with many issues open to argument. More specifically, certain arguments revolve around the inclusion of binary or N-ary representation of relationships in ER models. A central argument stems from the superior ability of N-ary modeling to reflect the true semantics of any given situation, whereas a binary model provides the simplest constructs for expressing information systems’ logical design and is equivalently represented in a relational database management system (DBMS) (McKee & Rodgers, 1992).