The coalgebraic perspective on objects and classes in object-oriented programming is elaborated: objects consist of a (unique) identifier, a local state, and a collection of methods described as a coalgebra; classes are coalgebraic (behavioural) specifications of objects. The creation of a "new" object of a class is described in terms of the terminal coalgebra satisfying the specification. We present a notion of "totally specified" class, which leads to particularly simple terminal coalgebras. We further describe local and global operational semantics for objects. Associated with the local operational semantics is a notion of bisimulation (for objects belonging to the same class), expressing observational indistinguishability. AMS Subject Classification (1991): 18C10, 03G30 CR Subject Classification (1991): D.1.5, D.2.1, E.1, F.1.1, F.3.0 Keywords & Phrases: object, class, (terminal) coalgebra, coalgebraic specification, bisimulation 1. Introduction Within the object-oriente...

TROLL light is a language for conceptual modeling of information systems. It is designed to describe the Universe of Discourse (UoD) as a system of concurrently existing and interacting objects. TROLL light objects have observable properties modeled by attributes, and the behavior of objects is described by events. Possible object observations may be restricted by constraints, whereas event occurrences may be restricted to specified life cycles. TROLL light objects are organized in an object hierarchy established by subobject relationships. Communication among objects is supported by event calling. Apart from introducing the various possibilities for the syntactical description of objects, we aim to describe how the state of an object community may be changed by event occurrences. 1 Introduction In recent years formal specification techniques have been receiving more and more attention (see for example [CHJ86, TM87, Win90]). Formal specifications are used for supporting the program an...

The envisaged notion of object is presented as corresponding to the basic, universal building block of (information) systems. A simple mathematical model for fully concurrent objects (actors) is adopted that extends a suitable model for sequential processes. An object is defined as a process possibly endowed with initiative and tracedependent attributes. Transactional requirements are analysed within this framework as liveness requirements. Object aggregation is explained using the general notion of object morphism. The basic inheritance, overriding and reification mechanisms are also presented, as well as a suitable notion of object-type. The computational model is shown through examples to provide a sound basis for (information) systems design, including abstract conceptual modeling and layered implementation of both passive (record-like) and active (procedure-like) objects. The model establishes a suitable semantic domain for the envisaged broad spectrum specification/design languag...

Order-sorted equational logic is extended with dynamic logic to a specification language for dynamic objects. Special attention is paid to different concepts of encapsulation that play a role in object-orientation. It is argued that the resulting language, CMSL, meets those requirements of the object-oriented database system manifesto [6] that are applicable to object-oriented conceptual models (as opposed to OO databases).

T ROLL is a language to specify information systems with dynamic behavior. Here, we elaborate on the specification of object aggregation in T ROLL . We distinguish between two kinds of aggregation, static and dynamic aggregation. Static aggregation means that the composition of objects is described using predicates over constant properties. Dynamic aggregation means that we may alter the composition of objects by invoking special operations (events) that are implicitly defined for each dynamic complex object. Additionally, we describe the specification of disjoint complex as a means for structuring a specification. We introduce language features to describe object aggregation and give some hints towards their semantics. 1 Introduction The first steps in an object-oriented approach to information system development concentrate on the abstract description of the relevant static and dynamic aspects of real-world objects (the Universe of Discourse, UoD) [Gri82, RBP + 90, Boo90] (concept...

The conceptual modeling of the Universe of Discourse (UoD) is an important phase for the development of information systems because the conceptual model is the basis for system development. Conceptual model specifications must be formal in order to be precise and unambiguous and to support consistency and completeness checks. The object-oriented paradigm is suitable for providing an integrated formal description of all relevant static and dynamic aspects of the UoD structured in objects. In this paper we introduce a formal concept of object suitable to represent the UoD by a collection of concurrent interacting objects. The Oblog-language for object-oriented UoD-specification based on this concept supports the integrated description of data about objects, the development of objects through time and of various relationships between objects taking into account static and dynamic aspects of object interaction. 1 Introduction Information systems are data-intensive software systems which ...

An object is a unit of structure and behavior; it has an identity which persists through change; objects communicate with each other; they are classified by object types, collected into object classes, related by inheritance, and composed to form complex objects. In the first part of the paper, this rich world of concepts and constructions is explained in an informal but systematic way, independent of any language or system. In the second part, features of an object specification language are outline which incorporate most of these concepts and constructions. 1 Introduction There are many languages, systems, methods and approaches in computing which call themselves "object--oriented", among them object--oriented programming languages like SmallTalk [GR83], C++ [St86] and Eiffel [Me88], object--oriented database systems like GemStone [BOS91], O 2 [De91], IRIS [Fi87] and ORION [Ki88], and object--oriented system development methods like GOOD [SS86], MOOD [Ke88] and HOOD [Hei88]. High--l...

The logic of norms, called deontic logic, has been used to specify normative constraints for information systems. For example, one can specify in deontic logic the constraints that a book borrowed from a library should be returned within three weeks, and that if it is not returned, the library should send a reminder. Thus, the notion of obligation to perform an action arises naturally in system specification.

. Within the KORSO project we have developed the object specification language TROLL light which allows to describe the part of the world to be modeled as a community of concurrently existing and communicating objects. Recently, we have worked out the basic notions of a pure algebraic semantics for our language. The main underlying idea is to present a transition system where the states represent the states of the specified information system, and state transitions are caused by the occurrence of finite sets of events. This semantics is formulated by representing states and state transitions as algebras. The various constructs of TROLL light are unified to general axioms restricting the possible interpretations for TROLL light object descriptions. 1 Introduction The information system development process can be divided into two phases: The requirements and the design engineering phase. At the end of the requirements engineering phase, a first formal description of the system to be dev...

In this paper, an approach to formally specify a conceptual model of a system and its environment to be developed in a behavior-oriented way is presented. We identify those concepts of object-oriented approaches that have to be formalized. We then propose characteristics of behavior-oriented mathematical models representing a system as a collection of interacting objects. To specify such models, we present the language T ROLL which is a formal object-oriented language for conceptual modeling. T ROLL avoids separate description of static and dynamic aspects of the system to be developed. Features of the language are explained using an example of a library information system. 1 Introduction A large number of software systems can be characterized as information systems. Information systems are capable of representing, storing, processing and producing information (i.e. data and knowledge) about a particular application domain, the Universe of Discourse (UoD). The early phases of informa...