A dedicated approach for the design and development of distributed software systems is outlined. The method may be used in combination with any standard object-oriented analysis and design method as far as static aspects are concerned. Dynamic aspects like the external behavior of distributed components, the status of services or resource handling, however, play the key role in distributed systems. The main contribution of the approach is to put its focus on these aspects right from the beginning of a design. ffl Information from static modeling is used to define the responsibilities for coordinating a system: classes coordinate their aggregates and explicit coordination objects are introduced to handle more complex relationships in order to prevent from introducing complex implicit (third-party carried) interdependencies between different parts of a system. ffl Interfaces of components extend the common signature specification by behavioral contracts consisting of pre/post-condition...

To ease the development of distributed systems, the visual notions for the structural aspects of object-oriented analysis and design should be combined with techniques handling concurrency and distribution. A novel approach and language for the visual design of distributed software systems is introduced and illustrated by means of an example. The language of OCoNs (Object Coordination Nets) is integrated into the structuring mechanisms of the UML [1] standard for object-oriented analysis and design. Such an object-oriented notation is crucial for handling complex software systems and can be extended with the graphical expressive power of Petri-Nets to also describe concurrency and coordination. The same visual language is used to specify the interfaces and contracts of software components, the resource handling within a component as well as the control flow of services. Keywords: visual language, object-orientation, contract, coordination, concurrency, PetriNets 2 CONTENTS Contents ...

: Based on Y. Shoham's paradigm, called Agent-Oriented Programming (AOP), multi-agentsystems are presented as a specialization of distributed, Object-Oriented systems. Equipped with knowledge, general concurrent inference mechanisms dealing with this knowledge, and a declarative agent program, these multi-agent-systems are intended to be a foundation of a new approach uniting advantages of many contributing areas: The precise semantics of Petri nets, the abstraction and encapsulation proposed in Object-Oriented approaches, and the power of logic programming, making it easy to adopt well-known AI-methods. As an example, an urban traffic information system will be designed which solves path searching problems in a distributed graph. Keywords: Multi-Agent-System, Agent-Oriented Programming, Distributed Artificial Intelligence, Distributed Object-Orientation, Coloured Petri Net. 1 Introduction In this paper, a representation of multi-agent-systems based on Coloured Petri nets will be int...

This paper informally introduces Object Petri Nets (OPNs) with a number of examples and discusses how this kind of Petri Net addresses a number of issues pertinent to Concurrent Object-Oriented Programming Languages. OPNs support a thorough integration of object-oriented concepts into Petri Nets, including inheritance and the associated polymorphism and dynamic binding. They have a single class hierarchy which includes both token types and subnet types, thereby allowing multiple levels of activity in the net. Yet OPNs retain the important property of being able to be transformed into behaviourally equivalent Coloured Petri Nets (CPNs), which can provide a foundation for adapting existing analysis techniques such as invariant analysis.

: Objects are studied as higher-level net tokens having an individual dynamical behaviour. In the context of Petri net research it is quite natural to also model such tokens by Petri nets. To distinguish them from the system net, they are called object nets. Object nets behave like tokens, i.e., they are lying in places and are moved by transitions. In contrast to ordinary tokens, however, they may change their state (i.e. their marking) when lying in a place or when being moved by a transition. By this approach an interesting and challenging two-level system modelling technique is introduced. Similar to the object-oriented approach, complex systems are modelled close to their real appearance in a natural way to promote clear and reliable concepts. Applications in fields like workflow, agent-oriented approaches (mobile agents and/or intelligent agents as in AI research) or open system networks are feasible. This paper gives a precise definition of the basic model together with a suitab...

One of the key issues of object-oriented modeling and design is inheritance. It allows for the definition of subclasses that inherit features of some superclass. Inheritance is well defined for static properties of classes such as attributes and methods. However, there is no general agreement on the meaning of inheritance when considering the dynamic behavior of objects, captured by their life cycles. This paper studies inheritance of behavior both in a simple process-algebraic setting and in a Petri-net framework. Process algebra is chosen, because it concentrates on behavior, while abstracting from the internal states of processes. The result of the algebraic study is a clear conceptual understanding of inheritance of behavior. It can be expressed in terms of blocking and hiding method calls. The results in the algebraic framework inspire the development of the concept of inheritance of behavior in the Petri-net framework. The Petri-net formalism allows for a graphical representation...

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: This paper informally introduces Object Petri Nets (OPNs) with a number of examples. OPNs support a thorough integration of object-oriented concepts into Petri Nets, including inheritance and the associated polymorphism and dynamic binding. They have a single class hierarchy which includes both token types and subnet types, thereby allowing multiple levels of activity in the net. The paper discusses some theoretical issues pertinent to the definition of OPNs, and compares the provisions of OPNs with those of other Concurrent Object-Oriented Programming Languages. The paper then considers a case study of using OPNs to model a cooperative editor for hierarchical diagrams. This extended example demonstrates the applicability of OPNs to the modelling of non-trivial concurrent systems. The methodology for deriving a Petri Net model is to adapt an object-oriented design methodology: the Object Model is prepared in Rumbaugh's OMT notation; the Dynamic Model is then prepared in the form of l...

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This paper focuses on a framework for representing a team plan and its projections on individual agents. The team plan is represented with a coloured Petri net. Using the implicit place reduction rule an agenticity hierarchy is deduced: each transition bearing two or more output places corresponds to splitting the (sub)team into (sub)subteams; a two-input-place transition merges subteams. The reduction rule is extended to support the notion of transfer of an agent from one subteam to another. These notions of splitting, merging and transfer are basic team management structures which describe the dynamic team hierarchical organisation. At each level of agenticity a plan is derived from the team plan reduction. Controlling an agent individually requires extracting individual information, such as activities involving the agent as well as interacting agents or subteams at each level of agenticity. The agent-projected plan encompasses for each level of agenticity an activity plan and a list of cooperating agents or subteams.