Abstract. 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).

Current modeling techniques are not well equipped to design dynamic software architectures. In this work we present the basic concepts for a dynamic architecture modeling using nets-within-nets. Netswithin-nets represent a powerful formalism that allows active elements, i.e. nets, to be nested in arbitrary and dynamically changeable hierarchies. Applying the concepts from nets-within-nets, therefore, allows us to model complex dynamic system architectures in a simple way, which enables us to design the system at different levels of abstractions using refinements of net models. Additionally to the conceptual modeling of such architecture, we provide a practical example where the concept has been successfully applied in the development of the latest release of Renew (Version 2 of the multiformalism Petri net IDE 1). The overall monolithic architecture has been exchanged with a system that is divided into a plug-in management system and plug-ins that provide functionality for the users. By combining plug-ins the system can be adapted to the users' needs. Through the introduction of the Petri net concepts, the new architecture is now-at runtime-dynamically extensible by registering plug-ins with the management system. The introduced architecture is applicable for any kind of architecture but most suitable for applications with dynamic structure.

Abstract. A multi-agent system has a high degree of concurrency. Petri nets are a well-established means for the description of concurrent systems. Reference nets are higher level, object-oriented Petri nets. With Renew (REference NEt Workshop), there exists a tool to model and execute reference nets with seamless Java integration. So, reference nets can be used to design executable multi-agent systems while hiding the sometimes annoying details of concurrent implementations in traditional programming languages. The technique is currently used to implement a FIPA-compliant agent platform for multi-agent systems (called CAPA) focused on retaining a maximum level of concurrency in the system.

In this work we present modeling techniques for the development of multi-agent applications within the reference architecture for multi-agent system Mulan. Our approach can be characterized as model driven development by using models in all stages and levels of abstraction regarding design, implementation and documentation. Both, standard techniques from software development as well as customized ones are used to satisfy the needs of multi-agent system development. To illustrate the techniques and models within this paper we use diagrams created during the development of an agent-based distributed Workflow Management System (WFMS).

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