W4: Modeling with Subtypes/Supertypes: Entity Generalization
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  Gordon Everest   Gordon C Everest
Professor Emeritus
University of Minnesota


Sunday, April 27, 2014
02:30 PM - 05:45 PM

Level:  Advanced

Entities, attributes, relationships, identifiers, and foreign keys are important data modeling constructs, particularly for relational databases, but subtypes and supertypes (S/Stypes) are even more important. Relational DBMSs do not handle S/Stypes. However, many data modeling CASE tools do include provision for S/Stypes, so data modelers need to understand how to properly use these constructs.

S/Stypes are truly essential for the data modeler (Graeme Simsion covered it early in his book, Data Modeling Essentials). They allow the database designer to defer choosing what objects to materialize or what (relational) tables to build until later in the database development process.

In the meantime, S/Stypes offer a means to formally represent overlapping entity/object populations at the very beginning of the design process. If you are not using S/Stypes in your data modeling, or want to deepen your understanding of these constructs, this session is for you. Knowledge and use of subtypes/supertypes should be in every data modeler's toolkit.

  • Situations which motivate the need for another data modeling construct
  • Definition of subtypes and supertypes - characteristics of a subtype-supertype "relationship"
  • Abstraction mechanisms: specialization vs. generalization; attribute vs. entity abstraction
  • Required conditions when using S/Stypes
  • The "universal relation" – the ultimate supertype (vs. no entity types at all!)
  • Distinguishing attribute(s) on the supertype: intensional vs. extensional sets
  • Declaring constraints on a subtype-supertype relationship
  • Inheritance in data models vs. inheritance and reuse in object-oriented design (they are not the same); inheritance priority, blocking, and overriding.

Dr. Everest is Professor Emeritus of MIS and Database in the Carlson School of Management at the University of Minnesota. With early "retirement," he continues to teach Advanced Data Modeling as an adjunct. His Ph.D. dissertation at the University of Pennsylvania Wharton School entitled "Managing Corporate Data Resources" became the text from McGraw-Hill, "Database Management: Objectives, System Functions, and Administration" in 1986.

Gordon has been teaching all about databases, data modeling, database management systems, data(base) administration, dimensional modeling, and data warehousing since he joined the university in 1970. Students learn the theory of databases and gain practical experience with real data modeling projects, with hands-on use of data modeling tools and DBMSs. Besides teaching about databases, he has helped many organizations do data modeling and design their databases. Actually doing it informs his teaching and presentations.

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