Abstract. We seek for a small set of primitives that might serve as a basis for formalizing 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 SCC's session handling mechanism allows for the definition of structured interaction protocols, more complex than the basic request-response 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 that relates our proposal with existing ones.

The interplay between process behaviour and spatial aspects of computation has become more and more relevant in Computer Science, especially in the field of collective adaptive systems, but also, more generally, when dealing with systems distributed in physical space. Traditional verification techniques are well suited to analyse the temporal evolution of programs; properties of space are typically not explicitly taken into account. We propose a methodology to verify properties depending upon physical space. We define an appropriate logic, stemming from the tradition of topological interpretations of modal logics, dating back to earlier logicians such as Tarski, where modalities describe neighbourhood. We lift the topological definitions to a more general setting, also encompassing discrete, graph-based structures. We further extend the framework with a spatial until operator, and define an efficient model checking procedure, implemented in a proof-of-concept tool.Related work. We use the terminology spatial logics in the "topological" sense; the reader should be warned that in Computer Science literature, spatial logics typically describe situations in which modal operators are interpreted syntactically, against the structure of agents in a process calculus (see [8,6] for some classical examples). The object of discussion in this research line are operators that quantify e.g., over the parallel subcomponents of a system, or the hidden resources of an agent. Furthermore, logics for graphs have been studied in the context of databases and process calculi (see [7,14], and references), even though the relationship with physical space is often not made explicit, if considered at all. The influence of space on agents interaction is also considered in the literature on process calculi using named locations [10]. Variants of spatial logics have also been proposed for the symbolic representation of the contents of images, and, combined with temporal logics, for sequences of images [11]. The approach is based on a discretisation of the space of the images in rectangular regions and the orthogonal projection of objects and regions onto Cartesian coordinate axes such that their possible intersections can be analysed from different perspectives. It involves two spatial until operators defined on such projections considering spatial shifts of regions along the positive, respectively negative, direction of the coordinate axes and it is very different from the topological spatial logic approach. A successful attempt to bring topology and digital imaging together is represented by the field of digital topology [21,24]. In spite of its name, this area studies digital images using models inspired by topological spaces, but neither generalising nor specialising these structures. Rather recently, closure spaces have been proposed as an alternative foundation of digital imaging by various authors, especially Smyth and Webster [22] and Galton [16]; we continue that research line, enhancing it with a logical perspective. Kovalevsky [18...

Abstract. 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.

Abstract. We address the specification and verification of spatio-temporal behaviours of complex systems, introducing Signal Spatio-Temporal Logic (SSTL). This modal logic extends the Signal Temporal Logic with spatial operators capable of specifying topological properties in a discrete space. The latter is modelled as a weighted graph, and provided with a boolean and a quantitative semantics. Furthermore, we define efficient monitoring algorithms for both the boolean and the quantitative semantics. These are implemented in a Java tool available online. We illustrate the expressiveness of SSTL and the effectiveness of the monitoring procedures on the formation of patterns in a Turing reaction-diffusion system.

No abstract

Cyber-Physical Systems (CPS) consist of collaborative, networked and tightly intertwined computational (logical) and physical components, each operating at different spatial and temporal scales. Hence, the spatial and temporal requirements play an essential role for their correct and safe execution. Furthermore, the local interactions among the system components result in global spatiotemporal emergent behaviors often impossible to predict at the design time. In this work, we pursue a complementary approach by introducing STREL a novel spatio-temporal logic that enables the specification of spatio-temporal requirements and their monitoring over the execution of mobile and spatially distributed CPS. Our logic extends the Signal Temporal Logic [15] with two novel spatial operators reach and escape from which is possible to derive other spatial modalities such as everywhere, somewhere and surround. These operators enable a monitoring procedure where the satisfaction of the property at each location depends only on the satisfaction of its neighbours, opening the way to future distributed online monitoring algorithms. We propose both a qualitative and quantitative semantics based on constraint semirings, an algebraic structure suitable for constraint satisfaction and optimisation. We prove that, for a subclass of models, all the spatial properties expressed with reach and escape, using euclidean distance, satisfy all the model transformations using rotation, reflection and translation. Finally, we provide an offline monitoring algorithm for STREL and, to demonstrate the feasibility of our approach, we show its application using the monitoring of a simulated mobile ad-hoc sensor network as running example.

Spatial aspects of computation are becoming increasingly relevant in Computer Science, especially in the field of collective adaptive systems and when dealing with systems distributed in physical space. Traditional formal verification techniques are well suited to analyse the temporal evolution of programs; however, properties of space are typically not taken into account explicitly. We present a topology-based approach to formal verification of spatial properties depending upon physical space. We define an appropriate logic, stemming from the tradition of topological interpretations of modal logics, dating back to earlier logicians such as Tarski, where modalities describe neighbourhood. We lift the topological definitions to the more general setting of closure spaces, also encompassing discrete, graph-based structures. We extend the framework with a spatial surrounded operator, a propagation operator and with some collective operators. The latter are interpreted over arbitrary sets of points instead of individual points in space. We define efficient model checking procedures, both for the individual and the collective spatial fragments of the logic and provide a proof-of-concept tool. 2012 ACM CCS: [Theory of computation]: Logic-Logic and verification / Modal and temporal logics / Verification by model checking; Semantics and reasoning; [Software and its engineering]: Software organization and properties-Software functional properties-Formal methods-Software verification;

We introduce a unifying framework to provide the semantics of process algebras, including their quantitative variants useful for modeling quantitative aspects of behaviors. The unifying framework is then used to describe some of the most representative stochastic process algebras. This provides a general and clear support for an understanding of their similarities and differences. The framework is based on State to Function Labeled Transition Systems, FuTSs for short, that are state-transition structures where each transition is a triple of the form (s, α, P). The first and the second components are the source state, s, and the label, α, of the transition, while the third component is the continuation function, P, associating a value of a suitable type to each state s . For example, in the case of stochastic process algebras the value of the continuation function on s represents the rate of the negative exponential distribution characterizing the duration/delay of the action performed to reach state s from s. We first provide the semantics of a simple formalism used to describe Continuous-Time Markov Chains, then we model a number of process algebras that permit parallel composition of models according to the two main interaction paradigms (multiparty and one-to-one synchronization). Finally, we deal with formalisms where actions and rates are kept separate and address the issues related to the co-existence of stochastic, probabilistic, and non-deterministic behaviors. For each formalism, we establish the formal correspondence between the FuTSs semantics and its original semantics.