A* Algebra for an Extended Object/Relational Model

The object relational data model [1,2,3] takes advantage of Codd's relational calculus power [5] and the object concept characteristics [6,7,11]. In fact, two major approaches have been adopted to satisfy the designers and users of the advanced databases. A revolutionary approach [3,7,13,15] which integrates the object characteristics into the new data models and where the specification of data constraints and the definition of interrogation language are considered as important research problems. The second one [2,22,24,48], called evolutionary approach, consists in preserving Codd's data model when being enriched by adequate concepts for the coverage of current applications in database. In this approach and compared with studies presented by Melton [18] and quoted by Gardarin [4], Date and Darwen have proposed in [1,2] the foundations of the object relational model. So, an algebra A consisted of first order logic operators has been defined to express various classes of querys in object relational database. This paper presents an extension of object relational model [1,2] to new types generated by operators.These operators, called Op, offer a means to specify domains as functions and allow consequently the increasing of data model expressivness. Concerning data query language, or more precisely the logical data calculation, the algebra A [1] is adapted and extended, giving A*, to support this extension of object relational model. Algebra A* contains algebraic operators which are able to support this new extension. Furthermore, to enhance the object relational model, the query language ERA* that implements A*, consists essentially in both logical calculation operators and new algebraic operators.