An Object Data Model Real-world Entities with Roles. When Constructing A

share completely the opinion of Richardson and Schwarz AN OBJECT DATA MODEL expressed in [7]: “Most object-oriented database systems display serious shortcoming in their ability to model both WITH ROLES 1 the dynamic nature and the many-faceted nature of common real-world entities. The most obvious example of this kind of entity is a person. While existing OODBSs may capture the notion that a student is a person, they do not support the A. Albano, R. Bergamini, G. Ghelli, R. Orsini notion that a given person may become a student. After graduation, that person ceases to be a student, and becomes an alumnus in the meantime, he or she may also be an Dipartimento di Informatica – Università di Pisa employee, a customer, a club member, etc. Throughout his Corso Italia 40, 56100 Pisa – Italy or her life, a person gains and loses many roles.” This problem has been investigated in the objectoriented database community by several authors, and we will comment on related works later on. The main contribution Abstract of this paper is the extension of an object-oriented data model with the notion of objects with roles, such that an Fibonacci is a strongly typed, object-oriented database object can have several roles and is always accessed through programming language with a new mechanism to model one of its roles. The behaviour of an object depends on the objects with roles. Traditional object-oriented programming role used to access it. Moreover this mechanism is supported languages do not have the possibility of changing by a strongly typed programming language Fibonacci which dynamically the type of an object to model the behaviour of also offers other features such as: a) the separation between real world entities which change their status over time. This the object interface, or type, and its implementation, to is a severe limitation in the context of a database allow the evolution of the implementation without affecting programming language. Besides this, traditional objectthe rest of the system which is only aware of the object oriented languages do not model the fact that the behaviour interface; b) the possibility of having different of real world entities may depend on the role that the entity implementations for a unique object type; c) the use of an plays in a context. We propose a mechanism to face both inclusion hierarchy with multiple inheritance to organize problems in the context of a statically strongly typed objectobject types. Besides objects, the data model provides also a oriented database programming language, and show that the class and association mechanism to model databases, but the two problems are strictly related. We show that the problem presentation of these mechanisms is outside the scope of this can be solved without giving up the most useful features of paper and can be found in [2]. object-oriented programming, namely inheritance, late The paper is organized as follows. Section 2 describes binding and encapsulation. Examples will be given referring the features of the proposed mechanism for objects with to the prototype implementation of the language. roles in a language independent fashion. Section 3 presents an overview of the Fibonacci type system to give the prerequisite to understand in Section 4 the constructs of the language to define objects with roles according to the requirements defined in Section 2. Section 5 compares the proposed solution with related works. In the conclusions, we 1 Background comment on our future plan.