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Abstract. There are several kinds of UML diagrams for convenient modelling of behaviour, but these diagrams can be hardly used for modelling mobility. The situation is not very different in the case of agent languages. There exist already some proposals for modelling mobility of interacting agents by graphical notations, but these notations are rather not very intuitive and hard to read if the specification becomes a bit complex. In this paper we propose a new graphical notation for modelling interaction of mobile objects. The notation is based on UML sequence diagrams. We model behaviour of mobile objects using a generalized version of lifelines. For different kinds of actions like creating, entering or leaving a mobile object we use stereotyped messages. We provide also a zoom-out, zoom-in facility allowing us to abstract from specification details. We explain our notation in a series of examples, study its applicability and limits.

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Abstract. Global systems -systems which may operate over transient networks including mobile elements and in which computation itself may be mobile -are gaining in importance. Nevertheless, the means for their modelling are still underdeveloped. The Unified Modelling Language (UML) is well developed for convenient modelling of behavior, but is not yet so useful for modelling aspects of design relevant to global systems, such as mobility. Non-functional requirements such as performance and security also assume an increased importance in the context of global systems, and here too, UML requires enhancement. In this paper we present an extension to UML class, sequence and activity diagrams to model mobile systems. We also describe extensions to model performance and security characteristics. We will describe how, wherever possible, we reuse existing work in these areas.

Abstract. The paradigm of contractual specification provides a transparent way of specifying systems. It clearly distinguishes between client and implementer obligations. One of the best known languages used for this purpose is OCL. Nevertheless, OCL does not provide primitives for a compact specification of what remains unchanged when a method is executed. In this paper, problems with specifying invariability are listed and some weaknesses of existing solutions are pointed out. The question of specifying invariability in OCL is studied and a simple but expressive and flexible extension is proposed. It is shown that this extension has a simple OCL based semantics.