Schlegelmilch, Jürgen (1999) Typesafe Dynamic Classification. Technical Report. Universität Rostock, Rostock.
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Abstract
Object-oriented systems rely on classification of objects as a basic principle. This classification can depend on the type of the object, or its state. Many systems, including almost all object-oriented programming languages, only support classification by type, making classes independent of state changes. Many application domains, however, use taxonomies based on classification by state. Views in database systems can achieve this kind of classification but object-oriented database systems do not accept these views as classes. The problem with classification by state is the need to reclassify objects after updates, and to maintain the type-safety in the presence of references to reclassified objects: if an object drops out of a class that a reference to it expects, then the reference is left ill-typed. Role models which allow explicit reclassification face the same problem. For SQL3, classification by state was considered but dropped in favour of mutability, substitutability, and static type checking; all four properties were considered incompatible but are not completely. Our proposal to handle the reclassification problem uses a powerful relationship mechanism instead of simple references. Relationships are multi-directional, thus allowing to find objects related to the reclassified one. We then either remove the link between the objects, or roll back the change that caused the reclassification. We also present an approach with less overhead that employs dynamic type checking. While the first approach allows to use views and role classes in the application schema, the second handles them for local variables in methods. We therefore combine both, which permits us to use view and role classes almost arbitrarily. This enables the important use of views in the schema to help maintaining consistency, as known from relational database systems. Finally, we discuss the combination of classification by properties, known as subclassing by constraining, and classification by type.
| Item Type: | Monograph (Technical Report) |
|---|---|
| Uncontrolled Keywords: | views, derived classes, classification, relationship, migration |
| Subjects: | Autorenart > DBIS-Publikationen Projekte > OSCAR |
| Depositing User: | Dbis Admin |
| Date Deposited: | 15 Jul 2016 11:02 |
| Last Modified: | 06 Jan 2018 13:50 |
| URI: | https://eprints.dbis.informatik.uni-rostock.de/id/eprint/744 |
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