Using the Guardian Programming Paradigm to Support Database Evolution.
Martin L. Kersten, Frans H. Schippers · Centrum Wiskunde & Informatica (CWI), the national research institute for mathematics and computer science in the Netherlands · 1986
A guardian is a high-level declarative description of a process which algorithmically reacts to an observed state or state change of a database.In this paper the role of guardians in the object-centered programming language Godel is illustrated.This language has been designed to support the construction of knowledge based applications and adaptive information systems.It is shown that traditional problems such as maintaining the integrity of a database is easily resolved using guardians without constraining the evolutionary paths of the database definition.This is accomplished by relaxation of the class membership rule found in objectoriented languages.In Godel class membership is a dynamic property determined by the provable characteristics of the object, rather then the operator applied to create the object.Dynamic class membership separates the classification of the object from its time-dependent semantic behavior.Therefore, integrity of the database can be preserved by a set of guardians which represent the integrity rules and react in an algorithmic fashion on any violation.