What is Object-Oriented Databases

Deductive object-oriented databases are intended to integrate the deductive and object-oriented database techniques to combine the best of two approaches and to overcome their inherent shortcomings, with a number of deductive object-oriented database languages proposed. However, most of these languages are only structurally object-oriented. Important behaviorally object-oriented features such as methods and encapsulation common in object-oriented database systems are not properly supported. This chapter presents a novel deductive object-oriented database language called ROL2 that extends structurally object-oriented database language ROL with all behaviorally object-oriented features. It supports in a rule-based framework all important object-oriented features such as object identity, complex objects, typing, information hiding, rule-based methods, encapsulation of such methods, overloading, late binding, polymorphism, class hierarchies, multiple structural and behavioral inheritance with overriding, blocking, and conflict handling. It is so far the only deductive object-oriented database language that supports all these features in a uniform rule-based framework.