Mobility induces new challenges for dynamic systems, which need a new conceptional treatment: systems, that deal for example with mobile agents, need extended security concepts to handle the risks, induced by foreign, untrusted agents. In this contribution we use object nets to model mobile systems. Object nets are Petri nets which have Petri nets as tokens – an approach known as the nets-withinnets paradigm. Object nets are called elementary if the net system has a two levelled structure. In this work we apply structural analysis methods for object nets – namely place invariants – to a simple case study modelling mobile agents.

Refinement of Petri nets is well suited for the hierarchical design of system models. It is used to represent a model at different levels of abstraction. Usually, refinement is a static concept. For many scenarios, however, it is desirable to have a more flexible form of refinement. For example in the context of service updates, e.g. version control in distributed systems, a mechanism for dynamic transition refinement is needed. The requirement of dynamic refinement at runtime is quite strong. Since we would like to redefine the system structure by itself, transition refinement cannot be implemented by a model transformation. Instead, an approach is needed which allows for dynamic net structures that can evolve as an effect of transitions firing. In previous work we introduced nets-within-nets as a formalism for the dynamic refinement of tokens. Here we consider an extension of nets-within-nets that uses special net tokens describing the refinement structure of transitions. Using this formalism it is possible to update refinements, introduce alternative refinements, etc. We present some formal properties of the extended formalism and introduce an example implementation for the tool Renew in the context of workflow modeling.

This contribution summarises the core results of the transdisciplinary ASKO project, part of the German DFG's programme Sozionik, which combines sociologists' and computer scientists' skills in order to create improved theories and models of artificial societies. Our research group has (a) formulated a social theory, which is able to explain fundamental mechanisms of self-organisation in both natural and artificial societies, (b) modelled this in a mathematical way using a visual formalism, and (c) developed a novel multi-agent system architecture which is conceptually coherent, recursively structured (hence non-eclectic) and based on our social theory. The article presents an outline of both a sociological middle-range theory of social self-organisation in educational institutions, its formal, Petri net based model, including a simulation of one of its main mechanisms, and the multi-agent system architecture SONAR. It describes how the theory was created by a re-analysis of some grand social theories, by grounding it empirically, and finally how the theory was evaluated by modelling its concepts and statements.

In this article I will prove undecidability results for elementary object net systems (EOS). Object nets are Petri nets which have Petri nets as tokens - an approach which is called the "netswithin-nets" paradigm. EOS are special object net systems which have a two leveled structure.

This paper studies mobile agents that act in a distributed name space. The difference between belonging to a name space (where objects can be accessed directly via pointers) and migrating between name spaces (where objects have to be treated as values, that can be copied into network messages) is taken account of by introducing Petri net based formalism, employing the nets-within-nets paradigm. This formalism, called mobile object nets, generalises the well-established theory of elementary object nets, which has seen many applications over the last decade. While mobile object nets provide a solution to the specific modelling problem mentioned above, they are much more generic and not restricted to this domain.

Agent oriented software engineering is seen as the approach taking object oriented approaches one step ahead. The design of agent systems is based on three fundamental perspectives: the functional, the team-interactional and the organisational perspective. The organisational perspective becomes a central design issue if the number of agents is large or the environment is unstable. While the functional perspective is well founded in the planning theory of artificial intelligence and the interactional perspective is rooted in the theory of speech-acts and formal ontologies, the organisational perspective is still an active research area with several open questions. In this paper we define a formal organisation model for agent systems based on Petri nets and show how agent oriented software engineering can benefit from this model.

Multi-agent system research deals with organization theoretical concepts in order to analyse and control supra-individual phenomena. However, there exists a conceptual gap between organizational specifications and their multi-agent implementation. We address this problem by presenting an integrated approach for the specification and deployment of organizational models based on Petri nets.

Refinement of Petri nets is well suited for the hierarchical design of system models. It is used to represent a model at different levels of abstraction. Usually, refinement is a static concept. For some inherent dynamic domains as for example the modelling of web services, we need a more flexible form of refinement, e.g. to bind web services at run-time. Run-time binding allows for a flexible orchestration of services. The requirement of dynamic refinement at run-time is quite strong. Since we would like to redefine the system structure by itself, transition refinement cannot be implemented by a model transformation. Instead, an approach is needed which allows for dynamic net structures that can evolve as an effect of transitions firing. In previous work we introduced nets-within-nets as a formalism for the dynamic refinement of tokens. Here we consider an extension of nets-within-nets that uses special net tokens describing the refinement structure of transitions. Using this formalism it is possible to update refinements, introduce alternative refinements, etc. We present some formal properties of the extended formalism and introduce an example implementation for the tool Renew.

Petri nets can be dualised by interchanging the role of places and transitions. This notion of duality is applicable only for unmarked Petri nets, since a marked place would be translated to a marked transition - which is meaningless - in the dual net. In this presentation we study the formalism of super-dual nets which are a generalisation of Petri nets. Super-dual nets allow for marked transitions also. The properties and the relation to other net formalism is studied.

Formalization of process behavior is a key issue for semantic Web services. However, this bears the disadvantage of clumsy specifications. In this paper we introduce a Petri net based approach to capture the semantics of Web services. It offers a visual modeling technique and means of refinement and composition. The model is very formal allowing for a clear specification of the semantics a process has. We combine ideas from the Petri net community with ideas from the description logic area focusing on ontologies

Dynamic service composition requires a formal description of the services Such that an agent can process these descriptions and reason about them. The amount of detail needed for an agent to grasp the meaning or a service may lead to clumsy specification.Petri nets offer a visual modeling technique for processes, that offers a refinement mechanism. Through this, a specification can be inspected on the level of detail needed for a given objective.In this paper we introduce a Petri net based approach to capture the semantics or services by combining Petri nets ideas from the description logic area focusing on ontologies. The resulting framework can than be used by agents to plan about activities involving services.

In this article I will prove undecidability results for elementary object net systems (Eos). Object nets are Petri nets which have Petri nets as tokens – an approach which is called the “nets-within-nets” paradigm. Eos are special object net system which have a two leveled structure.

The concept of mobile agents imposes a great security risk for information systems. In this paper we propose object nets as a specification formalism for multi-agent systems. Since the general formalism is Turing-powerful not every analysis method that is common for Petri net can be applied. So, we define the subclass of “ordinary” object nets that allows for the application of standard P/T-net techniques, i.e. the computation of boundedness, liveness etc.

Socionics attempts to release the architecture of multi-agent systems from the restrictive micro perspective viewpoint by the integration of the macro perspective in order to arrive at innovative agent systems. This paper shows how central research topics of sociology and computer science can be combined, in order to arrive at innovative agent systems. In the context of sociology the duality of micro and macro elements is relevant, while recursiveness of models appears in the perspective of computer science. These two elements are unified in our work to the socionic multi-agent architecture Sonar. The formal model, on which the representation bases, is the recursive formalism of reference nets—an extension of Petri nets that permits to understand nets again as tokens. With the help of these nets first of all a compact implementation of the multi-agent architecture Mulan is designed, secondly it serves as a description language for the sociological model, which is the fundament of Sonar. The main result here is to present an architecture based on Mulan and Sonar allowing to cover the micro as well as the macro perspective in agent-oriented modelling. Doing so, we introduce a scalable model based on agent systems.

The Petri-net-based formalism of mobile object-net systems (Mons) is used to model concurrent systems with dynamically changing environments, such as mobile objects. The tokens in Mons are themselves Petri nets, which gives the formalism an additional (vertical) dimension of nesting. Traditional Petri nets have essentially a horizontal structure, given by the fact that markings are multisets. The question arises, whether Mons can be regarded as a canonical extension of such Petri nets. Due to the nested nature of Mons, the answer is not obvious. We first give the formal definition of Mons and then prove some properties of the formalism, showing that, with respect to interleaving semantics (i.e. firing sequences), Mons can indeed be viewed as a canonical extension of traditional Petri nets. We then define Mons processes, also as a canonical extension of standard Petri net processes.

Renew is a computer tool that supports the development and execution of object-oriented Petri nets, which include net instances, synchronous channels, and seamless Java integration for easy modelling. Renew is available free of charge including the Java source code. Due to the growing application area more and more requirements had to be fulfilled by the tool set. Therefore, the architecture of the tool has been refactored to gain more flexibility. Now new features allow for plug-ins on the level of concepts (net formalisms) and on the level of applications (e.g. workflow or agents).

In this presentation the structure of formalisms are studied that allow Petri nets as tokens. The relationship towards common Petri net models and decidability issues are studied. Especially for ”elementary object-net systems” defined by Valk [x] the decidability of the reachability and the boundedness problem is considered. It is shown that reachability becomes undecidable while boundedness remains decidable for elementary object-net systems. Furthermore it is shown that even for minimal extensions the formalism obtains the power of Turing machines.

In this presentation the decidability issues of formalisms that allow Petri nets as tokens are studied. Especially for object-net systems defined by Valk the decidability of the reachability and the boundedness problem is considered. It is shown that reachability becomes undecidable while boundedness remains decidable for elementary object-net systems. Furthermore it is shown that even for minimal extensions the formalism obtains the power of Turing machines.

Mobility creates a new challenge for dynamic systems in all phases of the life cycle, like modelling, execution, and verification. In this work we apply the paradigm of “nets within nets” to this area since it is well suited to express the dynamics of open, mobile systems. The advantages of Petri nets — intuitive graphical representation and formal semantics — are retained and supplemented with a uniform way to model mobility and mobile (agent) systems. First the modelling of mobility is introduced in general, the results are carried forward to model mobility in the area of agent systems. The usefulness of the approach is shown in a second step by modelling a small case study, the implementation of a household robot system.