. It is claimed that object oriented databases (OODBs) overcome many of the limitations of the relational model. However, the formal foundation of OODB concepts is still an open problem. Even worse, for relational databases a commonly accepted datamodel existed very early on whereas for OODBs the unification of concepts is missing. The work reported in this paper contains the results of our first investigations on a formally founded object oriented datamodel (OODM) and is intended to contribute to the development of a uniform mathematical theory of OODBs. A clear distinction between objects and values turns out to be essential in the OODM. Types and Classes are used to structure values and objects repectively. Then the problem of unique object identification occurs. We show that this problem can be be solved for classes with extents that are completely representable by values. Such classes are called value-representable. Another advantage of the relational approach is the existence o...

We define an operational semantics and a type system for manipulating semistructured data that contains hidden information. The data model is simple labeled trees with a hiding operator. Data manipulation is based on pattern matching, with types that track the use of hidden labels.

In this paper we characterise exactly the complexity of a set based database language called SRL, which presents a unified framework for queries and updates. By imposing simple syntactic restrictions on it, we are able to express exactly the classes, P and LOGSPACE. We also discuss the role of ordering in database query languages and show that the hom operator of Machiavelli language in [OBB89] does not capture all the order-independent properties.

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This paper gives a detailed presentation of constraint satisfaction in the hybrid LAURE language. LAURE is an object-oriented language for Artificial Intelligence (AI) applications which allows the user to combine rules, constraints and methods that cooperate on the same objects in the same program. We illustrate why this extensibility is necessary to solve some large and difficult problems by presenting a real-life application of LAURE. We describe the syntax and the various modes in which constraints may be used, as well as the tools that are proposed by LAURE to extend constraint resolution. The resolution strategy as well as some implementation details are given to explain how we obtain good performances.

. It is claimed that object-oriented databases overcome many of the limitations of the relational data model especially by generalizing the notion of object identification. A clear distinction between objects and values turns out to be essential for the object-oriented approach whereas the relational model is based exclusively on values. Since, however, value uniqueness within scopes is a quite natural constraint for a wide class of applications, identification by value is also of interest for object-oriented datamodels. Hence, in this paper we concentrate on those classes where the extents are completely representable by values. We formalize some basic concepts of object-oriented databases and show that the finiteness of a database and the existence of finitely representable recursive types are sufficient to decide value-representability. Another advantage of the relational approach is the existence of structurally determined canonical update operations. We show that this property c...

It is claimed that object oriented databases (OODBs) overcome many of the limitations of the relational model. However, the formal foundation of OODB concepts is still an open problem. Even worse, for relational databases a commonly accepted datamodel existed very early on whereas for OODBs the unification of concepts is outstanding. Our research in Hamburg and Rostock is directed towards a formally founded object oriented datamodel (OODM) and to contribute to the development of a uniform mathematical theory of OODBs. This report contains the results of our first investigations on the OODM. A clear distinction between objects and values turns out to be essential in the OODM. Types and Classes are used to structure values and objects repectively. Then the problem of unique object identification occurs. We show that this problem can be be solved for classes with extents that are completely representable by values. Such classes are called valuerepresentable. The finiteness of a database and the existence of finitely representable rational tree types are sufficient to decide value-representability. Another advantage of the relational approach is the existence of structurally determined

Object oriented databases (OODBs) are composed of semi-independent objects but must also provide for the maintenance of inter-object consistency, especially with respect to constraints arising from class hierarchies and inter-object references. Hence the problem to provide consistent generic update methods. We address the problem how to derive such methods from the structure of an OODB schema by the specification of generator macros for them. These generators are based on a strict mathematical formalization of OODB concepts including the possibility to represent syntactic components of the language as values within the language itself, which is known to form the basis of linguistic reflection. Moreover, the approach can be extended to the enforcement of user-defined integrity constraints that give rise to context sensitive macros turning each user-defined method into branches of its greatest consistent specialization.

Solid theoretical foundations of object oriented databases (OODBs) are still missing. The work reported in this paper contains results on a formally founded object oriented datamodel (OODM) and is intended to contribute to the development of a uniform mathematical theory of OODBs. A clear distinction between objects and values turns out to be essential in the OODM. Types and classes are used to structure values and objects repectively. This can be founded on top of any underlying type system. We outline different approaches to type systems and their semantics and claim that OODB theory on top of arbitrary type systems leads to type theory with topos-theoretically defined semantics. On this basis the known solutions to the problems of unique object identification and genericity can be generalized. It turns out that extents of classes must be completely representable by values. Such classes are called value-representable. As a consequence object identifiers degenerate to a pure...

Conceptual modelling requires a solid mathematical theory of concepts concerning the collection of concepts used in a specific, but broad enough field. The field considered in this paper is database modelling. Here object orientation in the widest sense has been identified as a unifying conceptual umbrella that encompasses all relevant datamodels. The theory of object oriented databases has brought to light the fundamental distinction between the concepts of objects and values and correspondingly types and classes. This can be founded on top of any underlying type system. Thus, expressiveness of a datamodel basically depends on the type concept, from which the other concepts can be derived. In order to achieve a uniform mathematical theory we outline different type systems and their semantics and claim that OODB theory on top of arbitrary type systems leads to type theory with topos-theoretically defined semantics. On this basis the known solutions to the problems of unique ...