: Se/7/1994

This paper describes a model for developing applications of active object-oriented databases based on three orthogonal concepts; methods, guards and actions and a tool which implements these ideas called MGA. MGA objects are active; they have guards which constrain the object's state, actions which maintain database integrity when the object's state changes and methods through which the object provides other services. These active components are implemented as (collections of) rules and rules are in turn modelled as objects. Keywords: active databases, object-oriented databases, rule-based, forms. Introduction This paper describes MGA (Methods, Guards and Actions); a tool for the declarative specification of applications of an active object-oriented database (OODB). In MGA, an application is defined as an object class encapsulating attributes and methods. Application classes are active in the sense that they embody procedural semantics through methods and through actions triggered by w..