Class and Type Hierarchies: Extension, Constraining, and Roles

Schlegelmilch, Jürgen (1998) Class and Type Hierarchies: Extension, Constraining, and Roles. Technical Report. Universität Rostock, Rostock.


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With object-orientation, we model the world with objects and group objects with similar properties into classes. There are then two ways to build up a hierarchy of classes: extension adds new properties to create a subclass, while constraining restricts the values of existing properties. Programming languages support only subclassing by extension, but databases offer also subclassing by constraining via selection views. However, constraining is considered not type-safe because an object may change to no longer meet the selection criteria, thus leaving the view and dropping its type; references of this type to this object will then become invalid. We show that support for roles allows both modes to be combined into a database programming language. Classes defined by constraining are a special case of role classes, so supporting roles allows for constraining. Type-safety is achieved by using relationships instead of references.

Item Type: Monograph (Technical Report)
Uncontrolled Keywords: OODBMS, classification, reclassification, type, class, role, dynamic type
Subjects: Autorenart > DBIS-Publikationen
Depositing User: Dbis Admin
Date Deposited: 15 Jul 2016 08:58
Last Modified: 06 Jan 2018 13:42

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