Understanding Subtypes/Supertypes: the Data Modeler's Most Important Construct (Part 2)

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, so data modelers need to understand how to properly use these constructs. S/Stypes are important for the data modeler, who can now defer choosing what objects to materialize or what (relational) tables to build until later in the database development process. S/Stypes offer a means to formally represent overlapping entity/object populations at the 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.

• 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
• the "universal relation" (vs. no entity types at all!)
• single vs. multiple inheritance, or the type hierarchy vs. a type lattice
• declaring constraints on a subtype-supertype relationship
• how to design relational tables to represent a S/Stype relationship - mappings to a relational model
• inheritance in data models vs. inheritance and reuse in object-oriented design (they are not the same)
• inheritance priority, blocking, and overriding - how these concepts apply (or not)