ion Abstract: This paper seeks to establish within a formal framework how Coloured Petri Nets can be enhanced to produce Object Petri Nets. It does so by defining a number of intermediate Petri Net formalisms and identifying the features introduced at each step of the development. Object Petri Nets support a complete integration of object-oriented concepts into Petri Nets, including inheritance and the associated polymorphism and dynamic binding. In particular, Object Petri Nets have a single class hierarchy which includes both token types and subnet types. Interaction between subnets can be either synchronous or asynchronous depending on whether the subnet is defined as a super place or a super transition. The single class hierarchy readily supports multiple levels of activity in the net and the generation and removal of tokens has been defined so that all subcomponents are simultaneously generated or removed, thus simplifying memory management. Despite this descriptive power, Object...

Abstract. Object-oriented methodologies are increasingly used in software development. Despite the proposal of several formally based models, current object-oriented practice is still dominated by informal methodologies, like Booch, OMT, and UML. Unfortunately, the lack of dynamic semantics of such methodologies limits the possibility of early analysis of specifications. This paper indicates the feasibility of ascribing formal semantics to UML by defining translation rules that automatically map UML specifications to high-level Petri nets. This paper illustrates the method through the hurried philosophers problem, that is first specified by using (a subset of) UML, and then mapped onto high-level Petri nets. The paper indicates how UML specifications can be verified by discussing properties of the hurried philosophers problem that can be verified on the derived highlevel Petri net. 1

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 ...

Abstract. We propose to extend the CORBA interface definition of distributed objects by a behavioral specification based on high level Petri nets. This technique allows specifying in an abstract, concise and precise way the behavior of CORBA servers, including internal concurrency and synchronization. As the behavioral specification is fully executable, this approach also enables to early prototyping and testing of a distributed object system as soon as the behaviors of individual objects have been defined. The paper discusses several implementation issues of the multithreaded, distributed interpreter built for that purpose. The high level of formality of the chosen formalism allows for mathematical analysis of behavioral specifications. Keywords. Formal methods, distributed object-oriented systems, CORBA, Petri nets, behavioral specification. 1

This paper presents and formally defines the CO-OPN/2 formalism (Concurrent Object-Oriented Petri Net) which is devised for the specification of large concurrent systems. We introduce the basic principles of the formalism, and describe how some aspects of object-orientation -- such as the notions of class/object, object reference, inheritance and subtyping -- are taken into account. In CO-OPN/2, classes (considered as templates) are described by means of algebraic nets in which places play the role of attributes, and methods are external parameterized transitions. A semantic extension for the management of the object references is defined. Inheritance and subtyping are clearly distinguished. Interaction between objects consists of synchronizations. Synchronization expressions are provided which allow the designer to select interaction policies between the partners. We also provide a step semantics which expresses the true concurrency of the object behaviors. Finally, in orde...

The UML as standardized language for visual object-oriented modeling allows to capture the requirements as well as the structure and behavior of complex software systems. With the increasing demands of todays systems, behavior aspects like concurrency, distribution and reactivity become more important. But the language concepts of the UML for describing behavioral aspects are weak compared to its concepts for describing structures. Besides a lack of visual expressiveness, a deeper integration with the structure specification is missing. In order to close this gap, an expressive language for modeling object-oriented behavior is proposed with the OCoN approach. It describes contracts, object scheduling as well as control and data flow of services in a Petri-net-like form. A seamless visual embedding of contract specifications into service and object scheduling specifications is provided by different net types.

The aim of this paper is to briefly introduce the Concurrent Object-Oriented Petri Net specification language CO-OPN/2 which has overcome some limitations of its object-based ancestor CO-OPN. Classes are described by means of algebraic nets in which places play the role of attributes, and methods function as external parameterized transitions. Inheritance and sub-typing are distinguished, with the former is considered as a mechanism for reuse while the later is viewed on a semantic level, based on the substitutability principle with respect to the behavior of the objects. As in the CO-OPN language, cooperation between the objects is achieved by means of synchronization expressions which allow the designer to select object interaction policies.

A short introduction of reference nets is given together with a motivation of the basic ingredients of this net formalism: dynamic creation of net instances, references to other net instances as tokens, and communication between net instances via synchronous channels. An implementation in Java is presented that augments reference nets with Java expressions as arc and transition inscriptions. The resulting tool aims mainly at rapid prototyping and workow applications.

This paper presents a comparative survey of formalisms related to mobile agents. It describes the -calculus and its extensions, the Ambient calculus, Petri nets, Actors, and the family of generative communication languages. Each of these formalisms defines a mathematical framework that can be used to reason about mobile code; they vary greatly in their expressiveness, in the mechanisms they provide to specify mobile code based applications and in their practical usefulness for the validation and the verification of such applications. In this paper we show how these formalisms can be used to represent the mobility and communication aspects of two mobile code environments: Obliq and Messengers. We compare and classify the different formalisms with respect to mobility and discuss some shortcomings and desirable extensions. We also point to other emerging concepts in formalisms for mobile code systems.