multiple inheritance, or the type hierarchy vs. * various notational conventions for diagraming S/Stype relationships * required conditions when using S/Stypes entity abstraction (generalization) - some examples * characteristics of a subtype-supertype "relationship" * definition of subtypes and supertypes - one of several abstraction mechanisms * situations which motivate the need for another modeling construct In the meantime, S/Stypes offer a means to formally represent overlapping entity/object populations at the very beginning of the logical/conceptual design process. They allow the database designer to defer choosing what objects to materialize or what (relational) tables to build until later in the development process. S/Stypes are truly essential for the data modeler. Graeme Simsion got it right when he made it chapter 4, right up front in his book, Data Modeling Essentials, 3e, Morgan Kaufmann, 2005. In fact, they are not even mentioned in many introductory database textbooks or courses. We don't always hear or learn about S/Stypes. Most data modeling CASE tools include provision for S/Stypes, so data modelers need to understand how to properly use these constructs. However, subtypes and supertypes (S/Stypes) are even more important, particularly at the highest levels of logical or conceptual modeling. Well, they are important, particularly for relational database design (and most DBMS's today are relational). You may have thought that entities, attributes, relationships, identifiers, and foreign keys were the only important modeling constructs for the data modeler. The data modeler's most important construct
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