Mapping Generalizations and Specializations and Categories to Relational Databases

Abstract

An Entity Relationship (ER) model that includes all the concepts of the original ER model and the additional concepts of generalizations/specializations and categories is often referred to as the Extended ER (EER) model (Elmasri & Navathe, 2007). With the rising complexity of database applications, and also in light of today’s web data applications (Necasky, 2006), the basic concepts of the ER model, as originally developed by Chen(1976), are no longer sufficient. Hence the basic ER model has been extended to include generalizations and specializations (Bagui & Earp, 2003; Elmasri & Navathe, 2007), and the concept of categories (Elmasri, et al., 1985). In this short article we shed some light on these relationship concepts, concepts that database designers often find difficult to directly model (Engels et al., 1992/93). We also discuss the mapping rules for generalizations/specializations and categories. Important contributions in this area are also reported in (Elmasri et al., 1985; Gogolla & Hohenstein, 1991; Markowitz & Shoshani, 1992; Dey, et. al., 1999). Dullea, et. al. (2003) discusses the structural validity of modeling structures with ER models.