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...

Starting from a logic which specifies how to make deductions from a set of sentences (a `flat theory'), a way to generalise this to a partially ordered bag of sentences (a `structured theory') is given. The partial order is used to resolve conflicts. If OE occurs below / then / is accepted only insofar as it does not conflict with OE. We start with a language L, a set of interpretations M and a satisfaction relation fl ` M \Theta L. The key idea is to define, for each structured theory, a pre-order on interpretations. Models of the structured theory are defined to be maximal interpretations in the ordering. They are shown to exist if the logic hL; M; fli is compact. A revision operator is defined, which takes a structured theory and a sentence and returns a structured theory. The consequence relation has the properties of weak monotonicity, weak cut and weak reflexivity with respect to this operator, but fails their strong counterparts. 1 Introduction Ordering sentences in a theo...

An increasing volume of research in e-commerce is concerned with the development of tools and environments to support various aspects of business-to-business electronic contract formation and performance. This paper is mainly concerned with the latter and takes up the suggestion that automated execution of an agreement between (at least) two parties can be effected through a central control mechanism (a so-called e-marketplace). We revisit modal action logic to model an agreement as a state-based system and specify acceptable and unacceptable states of a business transaction. Unacceptable states result from violations of contractual obligations or prohibitions and call for appropriate recovery mechanisms to be specified, so that they can be enforced by the central control mechanism. We comment on the relations between contract violations (and their associated recovery mechanisms) and the concepts of fault tolerance and recovery arising in the broader distributed systems context, on the one hand, and contrary-to-duty structures from the (theoretical) deontic logic perspective, on the other.

This paper describes our experience in capturing, using a formal specification language, a model of the knowledge-intensive domain of oceanic air traffic control. This model is intended to form part of the requirements specification for a decision support system for air traffic controllers. We give an overview of the methods we used in analysing the scope of the domain, choosing an appropriate formalism, developing a domain model, and validating the model in various ways. Central to the method was the development of a formal requirements engineering environment which provided automated tools for model validation and maintenance

Increasingly, information systems development occurs in the context of existing systems and established organizational processes. Viewing organizational and system components as cooperating agents offers a way of understanding their inter-relationships and how these relationships would or should be altered as new systems are introduced. In this paper, we show how two agent-oriented frameworks can be used in combination during requirements engineering for cooperative information systems. The ALBERT language is used to specify requirements, in terms of states and actions, and information and perception. The i framework is used to understand and redesign organizational processes, in terms of strategic relationships and rationales. A small banking example is used to illustrate how the requirements process may iterate between the two levels of modelling and analysis towards a requirements specification. 1 Introduction Increasingly, information systems development occurs in the context...

A formalism is motivated and described for representing defaults in specifications. The formalism is called Ordered Theory Presentations. The ability to represent defaults narrows the gap between a customer 's initial requirements and a formal specification, and supports reuse on both a small and a large scale. We illustrate the issues throughout with reference to the lift example. We also consider the application of the formalism to specification revision. 1 Introduction Imagine specifying a lift system. There is a lift, with n buttons and n indicator lights inside, and there are doors. The buttons inside the lift are for requesting where the lift goes, and the indicator lights register such requests. There are floors, each with two buttons and indicator lights (one for requesting to go up and one for down). The indicator lights switch on in response to button pressings and off when the lift arrives at a floor; and the lift goes from floor to floor depending on the state of the ligh...

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The goal of this paper is to explain the usage and semantics of hierarchical defaults in logical specifications. We discuss the usefulness of defaults for different specification scenarios like specialization, aggregation, explanation, revision, etc. To understand defaults formally, we introduce a general framework parameterized on the underlying logical institution extended by an instantiation mechanism for formulae. It is shown that hierarchical defaults have intended models if the extended institution is compact. As an example for a non-standard logic, we give the semantics of defaults in the multi-modal object calculus of the is-core project. To structure and compose specifications with defaults, default-preserving specification morphisms are defined and corresponding colimit constructions are sketched. 1 Introduction In this paper, we want to explain the usage and semantics of defaults in logic-based system specifications, particularly in specifications having an object-oriented ...

The problem of developing software to meet precise specifications has lead to the development of mathematical notations for expressing and reasoning about the behaviour of a required or extant system. In this paper we describe a different use of formal models: as tools for gathering and consolidating requirements on interaction between engineered systems and their users. This change in focus reflects the growing use of sophisticated interactive technology in domains, such as medicine, where human comfort or safety is an issue. Not only must software systems function correctly, but the demands that the interface places on users of those systems need to be understood. This problem can not be addressed by formal models in isolation. Instead, we describe an approach that uses formal models of human information processing to augment models of system functions. As a result it becomes possible, at an early stage in system design, to consider the role of human cognition in the correct behaviou...

A conceptual model of a system is an explicit description of the behaviour required of the system. Methods for conceptual modelling include ER modelling, data flow modelling, JSD, and several object-oriented analysis methods. Given the current diversity of modelling methods, it is important for teaching as well as using these methods to know what the relationships between them is and to be able to indicate what the (im)possibilities of integrating different methods are. This paper compares three modelling methods (ER, data flow, JSD) on their possibilities for integration and combination. It is shown that there is a common core of these methods, which centers around the concept of system transaction and that unifies the static view of a system taken by ER modelling with the dynamic view taken by JSD and the functional view taken by data flow modelling. Several object-oriented analysis methods integrate these three views. This paper illustrates how this is done in the analysis stage of OMT. Finally, it is shown that the transaction decomposition table can be used as a pivot around which to combine different methods. The results of this paper can be used in teaching to explain the relationships and differences between the methods analysed here, and in system development practice to ease the transition from structured to objectoriented Appeared in The Computer Journal, 38(1), 1995, pages 17--30.