Collection Type Constructors in Entity-Relationship Modeling

Collections play an important part in everyday life. Therefore, conceptual data models should support collection types to make data modeling as natural as possible for its users. Based on the fundamental properties of endorsing order and multiplicity of its elements we introduce the collection types of rankings, lists, sets and bags into the framework of Entity-Relationship modeling. This provides users with easy-to-use constructors that naturally model different kinds of collections. Moreover, we propose a transformation of extended ER schemata into relational database schemata. The transformation is intuitive and invertable introducing surrogate attributes that preserve the semantics of the collection. Furthermore, it is a proper extension to previous transformations, and results in a relational database schema that is in Inclusion Dependency Normal Form. In addition, we introduce a uniqueness constraint that identifies collections uniquely and guarantees referential integrity at the same time.