CDOL: A comprehensive declarative object language. In this paper we present a rule-based database language known as CDOL (Comprehensive, Declarative Object Language) that is an integration of deductive, object-oriented and active database technology. CDOL provides sublanguages for the expression of derived data, constraints, updates and active rules. The rule-based query language of CDOL provides an expressive approach to extend the stored database with derived attributes and classes. The constraint sublanguage allows explicit declarative specification of integrity constraints as a basis for database consistency. The update sublanguage of CDOL enables ad-hoc declarative update requests, where updates are encapsulated in the methods associated with class definitions, thus conforming to traditional object-oriented design concepts. The active rule sublanguage provides active, user-transparent agents that support reactive behavior within CDOL applications. In particular, active rules can be used to supplement declarative updates to maintain database consistency with respect to the set of integrity constraints. Active rules in general are used to monitor the occurrence of specific events and to serve as alerters and triggers within a CDOL application. This paper presents the rule-based query language of CDOL and illustrates the manner in which the constraint, update and active rule sublanguages build on this declarative framework. The use of methods and transactions are also addressed, together with a discussion of the operational semantics of active rule processing.