Details

Autor(en) / Beteiligte

• Matthew West

Titel

12 - Classes

Ist Teil von

• Developing High Quality Data Models, 2011, p.137-149

Ort / Verlag

Elsevier Inc

Erscheinungsjahr

2011

Beschreibungen/Notizen

• A set is a thing that has members, and its identity is defined by its membership. This chapter takes a look at classes as sets in a general way and relates this to their use in data modeling as both entity types and data. There are two key relationships that it is important to distinguish—classification, where a thing is a member of a set, and specialization (or subtype/supertype), where all the members of the subtype are members of the supertype. This chapter provides an understanding of the different restrictions on set theory that may be found in different environments and demonstrates the process of recognizing them. Following this, it sheds light on the utility of powersets in the context of hierarchical sets, which commonly occur. Furthermore, it presents a high level data model for classes. A class is a set whose identity is defined by its membership and is at least non-well-founded. A specialization is a relationship where each member of the subclass is a member of the superclass. A specialization has exactly one subclass that is a class, and exactly one superclass that is a class. Finally, it presents a data model fragment that shows how the pattern derived from powersets can be applied to give flexibility to a data model, and this is illustrated by considering how this applies to physical properties and kinds of individual.