Recent Papers

• G. Ghelli, F. Nanni, G. Puglielli, A. Albano. Fibonacci Modules: A Modularization Mechanism for Object Databases . Interdata Project Technical Report T1-R39, 1999.

  An overview of the features of the Fibonacci type system is presented, with particular reference to those used in the definition of modules. The resulting module system is characterized by a high flexibility and expressivity, which is mainly due to the fact that modules are first class values. The paper describes Fibonacci module system and shows how these modules can be used to organize complex object databases in smaller, interrelated units.

• A. Albano, G. Antognoni, and G. Ghelli. View Operations on Objects with Roles for a Statically Typed Database Language. IEEE Transactions on Knowledge and Data Engineering, 12 (4), pages 548-567, July-August 2000

• A. Albano, G. Antognoni, and G. Ghelli. View Operations on Objects with Roles for a Statically Typed Database Language: The Type Rules and the Operational Semantics. Technical Report, Dipartimento di Informatica, Universita' di Pisa, 1999. (An extended version of the previous paper)

  To deal with the evolution of data and applications, and with the existence of multiple views for the same data, the object data model needs to be extended with two different sets of operations: object extension operations, to allow an object to dynamically change its type, and object viewing operations, to allow an object to be seen as if it had a different structure. In this paper a set of object viewing operations is defined in the context of a statically and strongly typed database programming language, which supports objects with roles, and the relationships with object extension and role mechanisms is discussed. We then show how the object viewing operations can be used to give the semantics of a higher level mechanism to define views for object databases. Finally, the formalization is included of both the type rules and the operational semantics of the language mechanisms presented.

• A. Albano, R. Bergamini, G. Ghelli, and R. Orsini. Fibonacci: A Programming Language for Object Databases.. Journal of Very Large Data Bases, 4 (3), 1995.

  Fibonacci is a statically and strongly typed, object-oriented database programming language incorporating new mechanisms to model databases in terms of objects with roles, classes and associations. A brief introduction to the language is provided to present those features which are particularly suited to modelling complex databases. Examples of its use are given referring to the prototype implementation of the language.

• A. Albano, M. Diotallevi, and G. Ghelli. Extensible Objects for Database Evolution: Language Features and Implementation Issues. Proc. of the Fifth Intl. Workshop on Data Base Programming Languages (DBPL), Gubbio, Italy, 1995.

  One of the limitations of commercially available object-oriented DBMSs is their inability to deal with objects that may change their type during their life and which exhibit a plurality of behaviours. Several proposals have been made to overcome this limitation. An analysis of these proposals is made to show the impact of more general modelling functionalities on the object implementation technique.

• A. Albano, R. Bergamini, G. Ghelli, and R. Orsini. An object data model with roles. In R. Agrawal, S. Baker, and D. Bell, editors, Proc. of the Nineteenth Intl. Conf. on Very Large Data Bases (VLDB) , Dublin, Ireland, pages 39-51, San Mateo, CA, 1993. Morgan Kaufmann.

  Fibonacci is a strongly typed, object-oriented database programming language with a new mechanism to model objects with roles. Traditional object-oriented programming languages do not have the possibility of changing dynamically the type of an object to model the behaviour of real world entities which change their status over time. This is a severe limitation in the context of a database programming language. Besides this, traditional object-oriented languages do not model the fact that the behaviour of real world entities may depend on the role that the entity plays in a context. We propose a mechanism to face both problems in the context of a statically strongly typed object-oriented database programming language, and show that the two problems are strictly related. We show that the problem can be solved without giving up the most useful features of object-oriented programming, namely inheritance, late binding and encapsulation. Examples will be given referring to the prototype implementation of the language.

• A. Albano, G. Ghelli, and R. Orsini. A relationship mechanism for a strongly typed object-oriented database programming language. In G.M. Lohman, A. Sernadas, and R. Camps, editors, Proc. of the Seventeenth Intl. Conf. on Very Large Data Bases (VLDB) , Barcelona, Spain, pages 565-576, San Mateo, CA, 1991. Morgan Kaufmann. European best paper award.

  Object-oriented data models are receiving wide attention since they provide expressive abstraction mechanisms to model naturally and directly both structural and behavioral aspects of complex databases applications. In an object- oriented data model, a database is modeled in terms of objects grouped in classes, organized into subclasses hierarchies. Moreover, associations between entities are modeled by defining properties of objects whose value is the related object. However this way of modeling associations has several limitations which make the description of some aspects of associations unnatural. To overcome these limitations an object-relationship data model is proposed which supports both the mechanisms of an object- oriented data model and a separate mechanism to model explicitly associations and to express declaratively common constraints on them. Constructs to support this model for a statically and strongly typed object-oriented database programming language are defined.