Two of the most studied extensions of trace and testing equivalences to nondeterministic and prob... more Two of the most studied extensions of trace and testing equivalences to nondeterministic and probabilistic processes induce distinctions that have been questioned and lack properties that are desirable. Probabilistic trace-distribution equivalence differentiates systems that can perform the same set of traces with the same probabilities, and is not a congruence for parallel composition. Probabilistic testing equivalence, which relies only on extremal success probabilities, is backward compatible with testing equivalences for restricted classes of processes, such as fully nondeterministic processes or generative/reactive probabilistic processes, only if specific sets of tests are admitted. In this paper, new versions of probabilistic trace and testing equivalences are presented for the general class of nondeterministic and probabilistic processes. The new trace equivalence is coarser because it compares execution probabilities of single traces instead of entire trace distributions, and turns out to be compositional. The new testing equivalence requires matching all resolutions of nondeterminism on the basis of their success probabilities, rather than comparing only extremal success probabilities, and considers success probabilities in a trace-by-trace fashion, rather than cumulatively on entire resolutions. It is fully backward compatible with testing equivalences for restricted classes of processes; as a consequence, the trace-by-trace approach uniformly captures the standard probabilistic testing equivalences for generative and reactive probabilistic processes. The paper discusses in full details the new equivalences and provides a simple spectrum that relates them with existing ones in the setting of nondeterministic and probabilistic processes.
Process algebras are a set of mathematically rigourous languages with well defined semantics that... more Process algebras are a set of mathematically rigourous languages with well defined semantics that permit modelling behaviour of concurrent and communicating systems. Verification of concurrent systems within the process algebraic approach can be performed by checking that processes enjoy properties described by some temporal logic’s formulae. In this paper we present a formal framework that permits verifying properties of concurrent and communicating systems by using an assumption-guarantee approach. Each system component is not considered in isolation, but in conjunction with assumptions about the context of the component. In the paper we introduce a sound and complete proof system that permits verifying whether a process, when it is executed in an environment for which we provide some assumptions, satisfies a given formula. It is also ensured that property satisfaction is preserved whenever the context is partially instantiated (implemented) as a concrete process that verifies the assumptions we have for the environment.
Klaim (Kernel Language for Agents Interaction and Mobility) is an experimental kernellanguage to ... more Klaim (Kernel Language for Agents Interaction and Mobility) is an experimental kernellanguage to model and program distributed concurrent applications with mobile code. Thelanguage consists of Linda-like primitives acting on multiple tuple spaces distributed over thenodes of a net, and of a set of operators for building processes that communicate via tuplespaces. However, the underlying model is at, namely nodes cannot
The wide-spreading of Internet has stimulated the introduction of new programming paradigms and l... more The wide-spreading of Internet has stimulated the introduction of new programming paradigms and languages that model interactions among hosts by means of mobile agents, and that are centered around the notions of location awareness. In this paper we show how to use formal tools, specifically a modal logic, for formalizing properties for mobile agent systems. We concentrate on one of these new languages, Klaim, and we use it to specify a system that permits maintaining the software installed on several heterogeneous computers distributed over a network by taking advantage of the mobile agent paradigm.
We describe a system that permits maintaining the software installed on several heterogeneous com... more We describe a system that permits maintaining the software installed on several heterogeneous computers distributed over a network by taking advantage of the mobile agent paradigm. The applications are installed and updated only on the central server. When a new release of an application is installed on the server, agents are scattered along the network to update the application on the clients.
The presence of Multiple Inheritance in a language raises subtle problems related to possible amb... more The presence of Multiple Inheritance in a language raises subtle problems related to possible ambiguities. To avoid handling these difficulties, many languages, including Java, do not support multiple inheritance. This paper studies the problem of implementing multiple inheritance in a class-based language that does not provide it. In particular we propose an experimental extension of Java, M-Java, which enables multiple inheritance, and a precompilation process translating M-Java programs into standard Java programs. This translation process is automatic and transparent to the programmer. The distinguishing feature of our proposal is that crucial semantic aspects of multiple inheritance, related to overriding and subtyping, are preserved by the translation process. We show that such aspects are not preserved in other alternative solutions, presented in the literature, which rely on simulating multiple inheritance by delegation techniques. We will also show that, due to language features, some problems still arise concerning protected methods.
KLAIM is an experimental programming language that supports a programming paradigm where both pro... more KLAIM is an experimental programming language that supports a programming paradigm where both processes and data can be moved across different computing environments. The language relies on the use of explicit localities. This paper presents a temporal logic for specifying properties of Klaim programs. The logic is inspired by Hennessy-Milner Logic (HML) and the µ−calculus, but has novel features that permit dealing with state properties and impact of actions and movements over the different sites. The logic is equipped with a complete proof system that enables one to prove properties of mobile systems.
Service-oriented computing is calling for novel computational models and languages with primitive... more Service-oriented computing is calling for novel computational models and languages with primitives for client-server interaction, orchestration and unexpected events handling. We present CaSPiS, a process calculus where the notions of session and pipelining play a central role. Sessions are two-sided and can be equipped with protocols executed by each side. Pipelining permits orchestrating the flow of data produced by different sessions. The calculus is also equipped with operators for handling (unexpected) termination of the partner’s side of a session. Several examples are presented to provide evidence for the flexibility of the chosen set of primitives. Our main result shows that in CaSPiS it is possible to program a “graceful termination” of nested sessions, which guarantees that no session is forced to hang forever after the loss of its partner.
In this paper we present an integration of PLinda, a probabilistic extension of Linda, and StoKla... more In this paper we present an integration of PLinda, a probabilistic extension of Linda, and StoKlaim, a stochastic extension of KLAIM. In the resulting language, StoPKlaim, the execution time of coordination primitives is modeled by means of exponentially distributed random variables, as in StoKlaim, the choice of the primitive to be executed among conflicting ones is thus resolved by the race condition principle, and the choice of the tuple to be retrieved by a single input/read operation in case of multiple matching tuples is governed by the weight-based probabilistic access policy of PLinda. The language represents a natural development and integration of previous results of the SENSORIA Project in the area of probabilistic and time-stochastic extensions of Tuple Space based coordination languages. The formal operational semantics of StoPKlaim is presented and an example of modeling is provided.
We present a Java software framework for building infrastructures to support the development of a... more We present a Java software framework for building infrastructures to support the development of applications for systems where mobility and network awareness are key issues. The framework is particularly useful to develop run-time support for languages oriented towards global computing. It enables platform designers to customize communication protocols and network architectures and guarantees transparency of name management and code mobility in distributed environments. The key features are illustrated by means of a couple of simple case studies.
Klaim is an experimental programming language that supports a programming paradigm where both pro... more Klaim is an experimental programming language that supports a programming paradigm where both processes and data can be moved across different computing environments. The language relies on the use of explicit localities, and on allocation environments that associate logical localities to physical sites. This paper presents a temporal logic for specifying properties of Klaim programs. The logic is inspired by Hennessy-Milner Logic (HML) and the ν-calculus, but has novel features that permit dealing with state properties to describe the effect of actions over the different sites. The logic is equipped with a consistent and complete proof system that enables one to prove properties of mobile systems.
A variant of Rate Transition Systems (RTS), proposed by Klin and Sassone, is introduced and used ... more A variant of Rate Transition Systems (RTS), proposed by Klin and Sassone, is introduced and used as the basic model for defining stochastic behaviour of processes. The transition relation used in our variant associates to each process, for each action, the set of possible futures paired with a measure indicating their rates. We show how RTS can be used for providing the operational semantics of stochastic extensions of classical formalisms, namely CSP and CCS. We also show that our semantics for stochastic CCS guarantees associativity of parallel composition. Similarly, in contrast with the original definition by Priami, we argue that a semantics for stochastic π-calculus can be provided that guarantees associativity of parallel composition.
We seek for a small set of primitives that might serve as a basis for formalising and programming... more We seek for a small set of primitives that might serve as a basis for formalising and programming service oriented applications over global computers. As an outcome of this study we introduce here SCC, a process calculus that features explicit notions of service definition, service invocation and session handling. Our proposal has been influenced by Orc, a programming model for structured orchestration of services, but the SCC's session handling mechanism allows for the definition of structured interaction protocols, more complex than the basic requestresponse provided by Orc. We present syntax and operational semantics of SCC and a number of simple but nontrivial programming examples that demonstrate flexibility of the chosen set of primitives. A few encodings are also provided to relate our proposal with existing ones.
Recently, specific attention has been devoted to the development of service oriented process calc... more Recently, specific attention has been devoted to the development of service oriented process calculi. Besides the foundational aspects, it is also interesting to have prototype implementations for them in order to assess usability and to minimize the gap between theory and practice. Typically, these implementations are done in Java taking advantage of its mechanisms supporting network applications. However, most of the recurrent features of service oriented applications are re-implemented from scratch. In this paper we show how to implement a service oriented calculus, CaSPiS (Calculus of Services with Pipelines and Sessions) using the Java framework IMC, where recurrent mechanisms for network applications are already provided. By using the session oriented and pattern matching communication mechanisms provided by IMC, it is relatively simple to implement in Java all CaSPiS abstractions and thus to easily write the implementation in Java of a CaSPiS process.
The structure of open nets, like the lnteroet, is highly dynamic, as the topology of component ne... more The structure of open nets, like the lnteroet, is highly dynamic, as the topology of component networks continuously evolves. In this context, node connectivity is a key aspect and a language for dis-Iributed network-aware mobile applications should provide explicit mechanisms to handle it. In this paper, we address the problem of expressing dynamic changes of node connectivity at linguistic level and, in particular, we focus on a slight extension of the language KLAIM, that is targeted to this aim. The extension consists of the introduction of a new category of processes that, in addition to the standard process operations, can execute a few new coordination operations for establishing new connections, accepting connection requests and removing connections. Our extension puts forward a clean separation between the coordinator level and the user level and, hence, it is modular enough to be easily applicable also to other network-aware languages. We will also show that our approach can be used as a guide for actual distributed (i.e. without a single centralized server) implementations of mobile systems.
A general framework for network aware programming is presented that consists of a language for pr... more A general framework for network aware programming is presented that consists of a language for programming mobile applications, a logic for specifying properties of the applications and an automatic tool for verifying such properties. The framework is based on X-KLAIM, eXtended KLAIM, an experimental programming language specifically designed to program distributed systems composed of several components interacting through multiple tuple spaces and mobile code. The proposed logic is a modal logic inspired by Hennessy-Milner logic and is interpreted over the same labelled structures used for the operational semantics of X-KLAIM. The automatic verification tool is based on a complete proof system that has been previously developed for the logic.
Two of the most studied extensions of trace and testing equivalences to nondeterministic and prob... more Two of the most studied extensions of trace and testing equivalences to nondeterministic and probabilistic processes induce distinctions that have been questioned and lack properties that are desirable. Probabilistic trace-distribution equivalence differentiates systems that can perform the same set of traces with the same probabilities, and is not a congruence for parallel composition. Probabilistic testing equivalence, which relies only on extremal success probabilities, is backward compatible with testing equivalences for restricted classes of processes, such as fully nondeterministic processes or generative/reactive probabilistic processes, only if specific sets of tests are admitted. In this paper, new versions of probabilistic trace and testing equivalences are presented for the general class of nondeterministic and probabilistic processes. The new trace equivalence is coarser because it compares execution probabilities of single traces instead of entire trace distributions, and turns out to be compositional. The new testing equivalence requires matching all resolutions of nondeterminism on the basis of their success probabilities, rather than comparing only extremal success probabilities, and considers success probabilities in a trace-by-trace fashion, rather than cumulatively on entire resolutions. It is fully backward compatible with testing equivalences for restricted classes of processes; as a consequence, the trace-by-trace approach uniformly captures the standard probabilistic testing equivalences for generative and reactive probabilistic processes. The paper discusses in full details the new equivalences and provides a simple spectrum that relates them with existing ones in the setting of nondeterministic and probabilistic processes.
Process algebras are a set of mathematically rigourous languages with well defined semantics that... more Process algebras are a set of mathematically rigourous languages with well defined semantics that permit modelling behaviour of concurrent and communicating systems. Verification of concurrent systems within the process algebraic approach can be performed by checking that processes enjoy properties described by some temporal logic’s formulae. In this paper we present a formal framework that permits verifying properties of concurrent and communicating systems by using an assumption-guarantee approach. Each system component is not considered in isolation, but in conjunction with assumptions about the context of the component. In the paper we introduce a sound and complete proof system that permits verifying whether a process, when it is executed in an environment for which we provide some assumptions, satisfies a given formula. It is also ensured that property satisfaction is preserved whenever the context is partially instantiated (implemented) as a concrete process that verifies the assumptions we have for the environment.
Klaim (Kernel Language for Agents Interaction and Mobility) is an experimental kernellanguage to ... more Klaim (Kernel Language for Agents Interaction and Mobility) is an experimental kernellanguage to model and program distributed concurrent applications with mobile code. Thelanguage consists of Linda-like primitives acting on multiple tuple spaces distributed over thenodes of a net, and of a set of operators for building processes that communicate via tuplespaces. However, the underlying model is at, namely nodes cannot
The wide-spreading of Internet has stimulated the introduction of new programming paradigms and l... more The wide-spreading of Internet has stimulated the introduction of new programming paradigms and languages that model interactions among hosts by means of mobile agents, and that are centered around the notions of location awareness. In this paper we show how to use formal tools, specifically a modal logic, for formalizing properties for mobile agent systems. We concentrate on one of these new languages, Klaim, and we use it to specify a system that permits maintaining the software installed on several heterogeneous computers distributed over a network by taking advantage of the mobile agent paradigm.
We describe a system that permits maintaining the software installed on several heterogeneous com... more We describe a system that permits maintaining the software installed on several heterogeneous computers distributed over a network by taking advantage of the mobile agent paradigm. The applications are installed and updated only on the central server. When a new release of an application is installed on the server, agents are scattered along the network to update the application on the clients.
The presence of Multiple Inheritance in a language raises subtle problems related to possible amb... more The presence of Multiple Inheritance in a language raises subtle problems related to possible ambiguities. To avoid handling these difficulties, many languages, including Java, do not support multiple inheritance. This paper studies the problem of implementing multiple inheritance in a class-based language that does not provide it. In particular we propose an experimental extension of Java, M-Java, which enables multiple inheritance, and a precompilation process translating M-Java programs into standard Java programs. This translation process is automatic and transparent to the programmer. The distinguishing feature of our proposal is that crucial semantic aspects of multiple inheritance, related to overriding and subtyping, are preserved by the translation process. We show that such aspects are not preserved in other alternative solutions, presented in the literature, which rely on simulating multiple inheritance by delegation techniques. We will also show that, due to language features, some problems still arise concerning protected methods.
KLAIM is an experimental programming language that supports a programming paradigm where both pro... more KLAIM is an experimental programming language that supports a programming paradigm where both processes and data can be moved across different computing environments. The language relies on the use of explicit localities. This paper presents a temporal logic for specifying properties of Klaim programs. The logic is inspired by Hennessy-Milner Logic (HML) and the µ−calculus, but has novel features that permit dealing with state properties and impact of actions and movements over the different sites. The logic is equipped with a complete proof system that enables one to prove properties of mobile systems.
Service-oriented computing is calling for novel computational models and languages with primitive... more Service-oriented computing is calling for novel computational models and languages with primitives for client-server interaction, orchestration and unexpected events handling. We present CaSPiS, a process calculus where the notions of session and pipelining play a central role. Sessions are two-sided and can be equipped with protocols executed by each side. Pipelining permits orchestrating the flow of data produced by different sessions. The calculus is also equipped with operators for handling (unexpected) termination of the partner’s side of a session. Several examples are presented to provide evidence for the flexibility of the chosen set of primitives. Our main result shows that in CaSPiS it is possible to program a “graceful termination” of nested sessions, which guarantees that no session is forced to hang forever after the loss of its partner.
In this paper we present an integration of PLinda, a probabilistic extension of Linda, and StoKla... more In this paper we present an integration of PLinda, a probabilistic extension of Linda, and StoKlaim, a stochastic extension of KLAIM. In the resulting language, StoPKlaim, the execution time of coordination primitives is modeled by means of exponentially distributed random variables, as in StoKlaim, the choice of the primitive to be executed among conflicting ones is thus resolved by the race condition principle, and the choice of the tuple to be retrieved by a single input/read operation in case of multiple matching tuples is governed by the weight-based probabilistic access policy of PLinda. The language represents a natural development and integration of previous results of the SENSORIA Project in the area of probabilistic and time-stochastic extensions of Tuple Space based coordination languages. The formal operational semantics of StoPKlaim is presented and an example of modeling is provided.
We present a Java software framework for building infrastructures to support the development of a... more We present a Java software framework for building infrastructures to support the development of applications for systems where mobility and network awareness are key issues. The framework is particularly useful to develop run-time support for languages oriented towards global computing. It enables platform designers to customize communication protocols and network architectures and guarantees transparency of name management and code mobility in distributed environments. The key features are illustrated by means of a couple of simple case studies.
Klaim is an experimental programming language that supports a programming paradigm where both pro... more Klaim is an experimental programming language that supports a programming paradigm where both processes and data can be moved across different computing environments. The language relies on the use of explicit localities, and on allocation environments that associate logical localities to physical sites. This paper presents a temporal logic for specifying properties of Klaim programs. The logic is inspired by Hennessy-Milner Logic (HML) and the ν-calculus, but has novel features that permit dealing with state properties to describe the effect of actions over the different sites. The logic is equipped with a consistent and complete proof system that enables one to prove properties of mobile systems.
A variant of Rate Transition Systems (RTS), proposed by Klin and Sassone, is introduced and used ... more A variant of Rate Transition Systems (RTS), proposed by Klin and Sassone, is introduced and used as the basic model for defining stochastic behaviour of processes. The transition relation used in our variant associates to each process, for each action, the set of possible futures paired with a measure indicating their rates. We show how RTS can be used for providing the operational semantics of stochastic extensions of classical formalisms, namely CSP and CCS. We also show that our semantics for stochastic CCS guarantees associativity of parallel composition. Similarly, in contrast with the original definition by Priami, we argue that a semantics for stochastic π-calculus can be provided that guarantees associativity of parallel composition.
We seek for a small set of primitives that might serve as a basis for formalising and programming... more We seek for a small set of primitives that might serve as a basis for formalising and programming service oriented applications over global computers. As an outcome of this study we introduce here SCC, a process calculus that features explicit notions of service definition, service invocation and session handling. Our proposal has been influenced by Orc, a programming model for structured orchestration of services, but the SCC's session handling mechanism allows for the definition of structured interaction protocols, more complex than the basic requestresponse provided by Orc. We present syntax and operational semantics of SCC and a number of simple but nontrivial programming examples that demonstrate flexibility of the chosen set of primitives. A few encodings are also provided to relate our proposal with existing ones.
Recently, specific attention has been devoted to the development of service oriented process calc... more Recently, specific attention has been devoted to the development of service oriented process calculi. Besides the foundational aspects, it is also interesting to have prototype implementations for them in order to assess usability and to minimize the gap between theory and practice. Typically, these implementations are done in Java taking advantage of its mechanisms supporting network applications. However, most of the recurrent features of service oriented applications are re-implemented from scratch. In this paper we show how to implement a service oriented calculus, CaSPiS (Calculus of Services with Pipelines and Sessions) using the Java framework IMC, where recurrent mechanisms for network applications are already provided. By using the session oriented and pattern matching communication mechanisms provided by IMC, it is relatively simple to implement in Java all CaSPiS abstractions and thus to easily write the implementation in Java of a CaSPiS process.
The structure of open nets, like the lnteroet, is highly dynamic, as the topology of component ne... more The structure of open nets, like the lnteroet, is highly dynamic, as the topology of component networks continuously evolves. In this context, node connectivity is a key aspect and a language for dis-Iributed network-aware mobile applications should provide explicit mechanisms to handle it. In this paper, we address the problem of expressing dynamic changes of node connectivity at linguistic level and, in particular, we focus on a slight extension of the language KLAIM, that is targeted to this aim. The extension consists of the introduction of a new category of processes that, in addition to the standard process operations, can execute a few new coordination operations for establishing new connections, accepting connection requests and removing connections. Our extension puts forward a clean separation between the coordinator level and the user level and, hence, it is modular enough to be easily applicable also to other network-aware languages. We will also show that our approach can be used as a guide for actual distributed (i.e. without a single centralized server) implementations of mobile systems.
A general framework for network aware programming is presented that consists of a language for pr... more A general framework for network aware programming is presented that consists of a language for programming mobile applications, a logic for specifying properties of the applications and an automatic tool for verifying such properties. The framework is based on X-KLAIM, eXtended KLAIM, an experimental programming language specifically designed to program distributed systems composed of several components interacting through multiple tuple spaces and mobile code. The proposed logic is a modal logic inspired by Hennessy-Milner logic and is interpreted over the same labelled structures used for the operational semantics of X-KLAIM. The automatic verification tool is based on a complete proof system that has been previously developed for the logic.
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Papers by Michele Loreti