Deductive Object-Oriented Databases

Deductive Object Oriented databases (DOODs) came about through the integration of the OO paradigm and logic programming. The following broad approaches have been adopted in the design of DOOD systems:
- Language Extension : An existing deductive language model is extended with object oriented features. For example, Datalog is extended to support identity, inheritance, and other OO features.
- Language Integration : A deductive language is integrated with an imperative programming language in the context of an object model or type system. The resulting system supports a range of standard programs, while allowing different and complementary programming paradigms to be used for different tasks, or for different parts of the same task.
- Language Reconstruction : An object model is reconstructed, creating a new logic language that includes object-oriented features. in this strategy, the goal is to develop an object logic that captures the essentials of the object-oriented paradigm and that can also be used as a deductive programming language in DOODs.

Validity combines deductive capabilities with the ability to manipulate complex objects. The ability to declaratively specify knowledge as deduction and integration rules brings knowledge independence. Moreover, the logic-based language of deductive databases enables advanced tools, such as those for checking the consistency of a set of rules, to be developed. VALIDITY provides the following :
- A DOOD data model and language, called DEL (Datalog Extended Language).
- An engine working along a client-server model.
- A set of tools for schema and rule editing, validation, and querying.

The DEL data model provides object-oriented capabilities, similar to those offered by the ODMG data model, and includes both declarative and imperative features. The declarative features include deductive and integrity rules, with full recursion, stratified negation, disjunction, grouping, and quantification. The imperative features allow functions and methods to be written.