A Taxonomy of Recursive Relationships and Their Structural Validity in ER Modeling

In this paper, we present the complete classification of recursive relationships and the criteria that contribute to the structural validity of modeling recursive relationships within the entity-relationship (ER) diagram. Unlike typical other analyses that use only maximum cardinality constraints, we have used both maximum and minimum cardinality constraints in defining the properties and their structural validity criteria. We used the notions of role uniqueness, path connectivity, and cardinality constraints to derive a complete and comprehensive set of decision rules. Five rules and three corollaries were established to determine structural validity of recursive relationships. The contribution of this paper is to present a complete taxonomy of recursive relationships with their properties as well as the decision rules for their structural validity. These decision rules can be readily applied to real world data models regardless of their complexity. The rules can easily be incorporated into the database modeling and designing process, or extended into case tool implementations.