Project code: DEGAS
Research group: Database Architectures and Information Access (INS1)

Project coordinator: Arno Siebes

DEGAS is an active, temporal, object-oriented data model currently under development at CWI.This work is funded by SION, the Foundation for Computer Science Research in the Netherlands through the project A Design Theory for Autonomous Databases. DEGAS aims at complete integration of static and dynamic aspects of a system. This is achieved through complete encapsulation of structure and behaviour in autonomous objects. The behaviour of an autonomous object has three components: methods, lifecycles, and rules. The structure of a DEGAS object is given by its attributes.

Rules in DEGAS are ECA rules in the tradition of active databases. DEGAS also incorporates elements from temporal databases through an object history. This means that the state of an object is its complete history.

Objects can be extended dynamically through an addon mechanism. Addons can add all elements of an object's specification. This mechanism, in combination with relations in DEGAS, make DEGAS a good platform for the implementation of roles.

Object autonomy also means that we try to have as little central control as possible in a system. Among the arguments against central control are massively parallel computer systems, interorganisational information systems and networked systems with rapidly changing topologies. Sometimes central control is infeasible and sometimes it is undesirable. Thus, systems built of autonomous components are necessary for these, extremely distributed, information systems.

Members
Johan van den Akker, Arno Siebes

Key publications
Complete list of publications associated with this project

Group reports

• DEGAS: A temporal active data model based on object autonomy
  J.F.P. van den Akker, A.P.J.M. Siebes
  1996, CS-R9608, ISSN 0169-118X
  This report defines DEGAS, an advanced active data model that is novel in two ways. The first innovation is object autonomy, an extreme form of distributed control. In comparison to more traditional approaches, autonomous objects also encapsulate rule definitions to make them active. The second innovation of DEGAS is its temporal aspect. Active databases have an inherent temporal element in the specification and detection of event patterns that trigger rules.
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• (Un)decidability results for trigger design theories
  A.P.J.M. Siebes, J.F.P. van den Akker, M.H. van der Voort
  1995, CS-R9556, ISSN 0169-118X
  Active databases are databases extended with production rules or triggers. Triggers have different uses in databases. Originally they were devised as a more flexible method of constraint enforcement.Triggers have found a much wider use however, because it is possible to code all dynamics of an information system in database triggers.Such use results in the presence of large sets of triggers in an active database. The mutual interaction of triggers in a set can lead to undesired results such as non-termination of trigger execution. To enable us to analyse a trigger set in advance for such behaviour we need a design theory for database triggers. In this report we consider a number of predicates on trigger sets.
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DEGAS is an acronym for Dynamic Entities Get Autonomous Status. More importantly, it follows the popular tradition of naming database systems after French painters. Since our group already had a system named Monet, we named our system after the painter Degas.