In this paper, we argue that object-oriented models must be able to represent three kinds of taxonomic structures: static classes, dynamic classes, and role classes, that behave differently with respect to object migration. If CAR is a static subclass of V EHICLE, then a vehicle that is not a car can never migrate to the CAR subclass. On the other hand, if EMP loyee is a dynamic subclass of PERSON object class, then a PERSON that is not an employee may migrate to EMP . In both cases, an instance of the subclass is identical to an instance of the superclass. By contrast, if EMP is modeled as a role class of PERSON , then every employee differs from every person, but a PERSON instance can acquire one or more EMP instances as roles. The distinctions between the three kinds of classes are orthogonal, so that we can have, for example, dynamic subclasses of object or role classes, or role classes of dynamic or static classes. The paper is divided into two parts. In the first, infor...

In this paper, we argue that object-oriented models must be able to represent three kinds of taxonomic structures: static subclasses, dynamic subclasses and role classes. If CAR is a static subclass of V EHICLE, then a vehicle that is not a car can never migrate to the CAR subclass. If EMP loyee is a dynamic subclass of PERSON , then a PERSON that is not an employee may migrate to EMP . In both cases, an instance of the subclass is identical to an instance of the superclass. Finally, if EMP is modeled as a role class of PERSON every employee differs from every person, but a PERSON instance can acquire one or more EMP instances as roles. We outline an approach to formalizing these taxonomic structures in order-sorted dynamic logic with equality. Keywords: Theoretical foundations, formal methods, OO analysis and design February 2, 1994 Contents 1 Introduction 1 2 Methodological aspects of role-playing and class migration 1 2.1 Object classification and identification : : : : : : : : :...

One part of the task in presenting a semantics for a natural language is to show how the meanings of the constituents of a sentence are combined with one another to build up a meaning for the whole sentence. To a certain degree, this part of the task can be worked on without committing oneself too specifically to any particular theory of meaning, and that is what I am going to try to do here. The construction of interest is that of generic sentences. Such sentences are found in all natural languages (though not in all artificial languages), but I will confine my remarks to how English generic sentences are built up from constituent meanings, ever hopeful that what I have to say about English will shed light on similar constructions in a wider range of natural languages. I will begin by giving a series of descriptions of what generic sentences are, working from the most notional and towards the most linguistic, to first stake out the domain of inquiry. I then turn to the semantic composition of such sentences, arguing that they are not uniformly of subject-predicate form, but that a wider variety of

In this paper we investigate several concepts that are known in database research for some time but which are still surrounded by some confusion. We start with the concepts of object identifier, surrogate and key and list the differences between these concepts, which in practice are often ignored. Sharpening these differences allows us to analyze the distinction between objects and roles that recently surfaced in the literature. Distinguishing objects from roles helps to avoid migration of objects between classes and thus the problems associated with it. We show that this distinction requires the use of role identifiers that, just as object identifiers, should be globally unique and unchangeable. We next show that using role identifiers requires a distinction between two essentially different kinds of inheritance relationships, is-a inheritance and played-by inheritance. These are often both treated as if they were one and the same kind of is-a relationship. The result of the discussio...