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We propose a sound and complete axiomatisation of a class of graphs with nesting and either locally or globally restricted nodes. Such graphs allow to represent explicitly and at the right level of abstraction some relevant topological and logical features of models and systems, including nesting, hierarchies, sharing of resources, and pointers or links. We also provide an encoding of the proposed algebra into terms of a gs-monoidal theory, and through these into a suitable class of ″wellscoped″ term graphs, showing that this encoding is sound and complete with respect to the axioms of the algebra. [ABSTRACT FROM AUTHOR]

We define an algebraic theory of hierarchical graphs, whose axioms characterise graph isomorphism: two terms are equated exactly when they represent the same graph. Our algebra can be understood as a high-level language for describing graphs with a node-sharing, embedding structure, and it is then well suited for defining graphical representations of software models where nesting and linking are key aspects. [ABSTRACT FROM AUTHOR]

Rule-based specifications have been very successful as a declarative approach in many domains, due to the handy yet solid foundations offered by rule-based machineries like term and graph rewriting. Realistic problems, however, call for suitable techniques to guarantee scalability. For instance, many domains exhibit a hierarchical structure that can be exploited conveniently. This is particularly evident for composition associations of models. We propose an explicit representation of such structured models and a methodology that exploits it for the description and analysis of model- and rule-based systems. The approach is presented in the framework of rewriting logic and its efficient implementation in the rewrite engine Maude and is illustrated with a case study. [ABSTRACT FROM AUTHOR]

We propose a class of hierarchical graphs equipped with a simple algebraic syntax as a convenient way to describe configurations in languages with inherently hierarchical features such as sessions, fault- handling scopes or transactions. The graph syntax can be seen as an intermediate representation language, that facilitates the encoding of structured specifications and, in particular, of process calculi, since it provides primitives for nesting, name restriction and parallel composition. The syntax is based on an algebraic presentation that faithfully characterises families of hierarchical graphs, meaning that each term of the language uniquely identifies an equivalence class of graphs (modulo graph isomorphism). Proving soundness and completeness of an encoding (i.e. proving that structurally equivalent processes are mapped to isomorphic graphs) is then facilitated and can be done by structural induction. Summing up, the graph syntax facilitates the definition of faithful encodings, yet allowing a precise visual representation. We illustrate our work with an application to a workflow language and a service-oriented calculus. [ABSTRACT FROM AUTHOR]

A number of formalisms have been defined to support the specification and analysis of service oriented applications. These formalisms have been equipped with tools (types or logics) to guarantee the correct behavior of the specified services. Due to the semantic gap between the specification formalism and the programming languages of service oriented overlay computers a critical issue is guaranteeing that correctness is preserved when running the specified systems over available implementations. We have defined a service oriented abstract machine, equipped with a formal structural semantics, that can be used to implement service specification formalisms. We use our abstract machine to implement different service oriented formalisms that have been recently proposed, each posing specific challenges that we can address successfully. By exploiting the SOS semantics of the abstract machine and those of the considered service oriented formalisms we do prove that our implementations are correct (sound and complete). We also discuss possible implementations of other formalisms. [ABSTRACT FROM AUTHOR]

Reo is an exogenous coordination model for software components. The informal semantics of Reo has been matched by several proposals of formalization, exploiting co-algebraic techniques, constraint-automata, and coloring tables. We aim to show that the Tile Model offers a flexible and adequate semantic setting for Reo, such that: (i) it is able to capture context-aware behavior; (ii) it is equipped with a natural notion of behavioral equivalence which is compositional; (iii) it offers a uniform setting for representing not only the ordinary execution of Reo systems but also dynamic reconfiguration strategies. [ABSTRACT FROM AUTHOR]

Application or business logic, used in the development of services, has to do with the operations that define the application functionalities and not with the platform ones. Often security problems can be found at this level, because circumventing or misusing the required operations can lead to unexpected behaviour or to attacks, called application logic attacks. We investigate this issue, by using the CaSPiS calculus to model services, and by providing a Control Flow Analysis able to detect and prevent some possible misuses. [ABSTRACT FROM AUTHOR]

It is widely recognised that process calculi stay to concurrent computing as lambda-calculus stays to sequential computing; in fact, they lay abstract, rigorous foundations for the analysis of interactive, communicating systems. Nowadays, the increasing popularity of Service-Oriented Computing (SOC) challenges the quest for novel abstractions tailored to the well-disciplined handling of specific issues, like long running interactions, orchestration, and unexpected events. In fact, these features emerge neatly in most SOC applications and need to be studied as first-class aspects, whereas they would be obfuscated if dealt with by sophisticated encoding in traditional process calculi. This paper overviews some of the most recent proposals emerged in the literature, pointing out their main characteristics and presents in more detail one such proposal, called CaSPiS, by providing several examples to give evidence of its flexibility. No prior acquaintance with process calculi is assumed, indeed a gentle introduction to their basics is provided before the more advanced material be presented. [ABSTRACT FROM AUTHOR]

We present a UML Profile for the description of service oriented applications. The profile focuses on style-based design and reconfiguration aspects at the architectural level. Moreover, it has formal support in terms of an approach called Architectural Design Rewriting, which enables formal analysis of the UML specifications. We show how our prototypical implementation can be used to analyse and verify properties of a service oriented application. [ABSTRACT FROM AUTHOR]

Service oriented applications feature interactions among several participants over the network. Mechanisms such as correlation sets and two-party sessions have been proposed in the literature to separate messages sent to different instances of the same service. This paper presents a process calculus featuring dynamically evolving multiparty sessions to model interactions that spread over several participants. The calculus also provides primitives for service definition/invocation and for structured communication in order to highlight the interactions among the different concepts. Several examples from the SOC area show the suitability of our approach. [ABSTRACT FROM AUTHOR]

The notion of a session is fundamental in service-oriented applications, as it serves to separate interactions between clients and different instances of the same service, and to group together logical units of work. Recently, the Service Centered Calculus (SCC) has been proposed as a process calculus designed around the concept of a dyadic session between a service side and an invoker side, where interaction protocols and service orchestration can be conveniently expressed. In this paper we propose a generic type system to collect services΄ behaviours and then we fix a class of well-typed processes that are guaranteed to be deadlock free, in the sense that they either diverge by invoking new service instances or reach a normal form. The type system is based on previous research on traditional mobile calculi, here conveniently extended and simplified thanks to the neat discipline imposed by the linguistic primitives of SCC. [ABSTRACT FROM AUTHOR]

We propose Architectural Design Rewriting (ADR), an approach to formalise the development and reconfiguration of software architectures based on term-rewriting. An architectural style consists of a set of architectural elements and operations called productions which define the well-formed compositions of architectures. Roughly, a term built out of such ingredients constitutes the proof that a design was constructed according to the style, and the value of the term is the constructed software architecture. A main advantage of ADR is that it naturally supports style-preserving reconfigurations. The usefulness of our approach is shown by applying ADR to SRML, an emergent paradigm inspired by the Service Component Architecture. We model the complex operation that composes several SRML modules in a single one by means of suitable rewrite rules. Our approach guarantees that the resulting module respects SRML΄s metamodel. [ABSTRACT FROM AUTHOR]

We illustrate two ways to address the specification, modelling and analysis of dynamic software architectures using: i) ordinary typed graph transformation techniques implemented in Alloy; ii) a process algebraic presentation of graph transformation implemented in Maude. The two approaches are compared by showing how different aspects can be tackled, including representation issues, modelling phases, property specification and analysis. [ABSTRACT FROM AUTHOR]

Ugo΄s research activity in the area ofModels of Computation (MoC, for short) has been prominent, influential and broadly scoped. Ugo΄s trademark is that undefinable ability to understand and distill computational aspects into new models as if you were reading them out of some evident connection between well-know models: only, most often, that connection is really visible only after Ugo shows the way. Like experienced sailors have trusted compasses and sextants to help them find the best routes to harbour, Ugo relies on a bag of favourite tools which he has used along the years to deliver a variety of contributions to the MoC area. To mention just three (in alphabetic order): algebraic techniques, concurrency theory, and unification mechanisms. In this introductory contribution we would like to recall some of the influentialMoC models put forward by Ugo which cut across the three approaches. Before doing that, it is worth devoting some space to discuss the three aspects separately. Notably, the use of category theory is a pervasive common trait. [ABSTRACT FROM AUTHOR]

We present a simple parametric calculus of processes which exchange mobile code, where type safety is ensured by a combination of static and dynamic checks. That is, internal consistency of each process is locally verified before starting execution, by only relying on type assumptions on missing code; then, at execution time, when locally typechecked code is sent from a process to another, a run-time check based on a subtyping relation ensures that it can be successfully received, without requiring to inspect code again. The calculus is defined in a parametric way, that is, we do not fix some ingredients which can vary depending on the specific language or system. Notably, we abstract away from the specific nature of the code to be exchanged, and of the static and dynamic checks. We formalize the notion of type safety in our general framework and provide sufficient conditions on the above ingredients which guarantee this property. We illustrate our approach first on a simple lambda-calculus with records, and then on a calculus of mixin modules which generalizes the previous one. [ABSTRACT FROM AUTHOR]

We present a powerful and flexible method for automatically checking anonymity in a possibilistic general-purpose process algebraic verification toolset. We propose new definitions of a choice anonymity degree and a player anonymity degree, to quantify the precision with which an intruder is able to single out the true originator of a given event or to associate the right event to a given protocol participant. We show how these measures of anonymity can be automatically calculated from a protocol specification in μCRL, by using a combination of dedicated tools and existing state-of-the-art μCRL tools. To illustrate the flexibility of our method we test the Dining Cryptographers problem and the FOO 92 voting protocol. Our definitions of anonymity provide an accurate picture of the different ways that anonymity can break down, due for instance to coallitions of inside intruders. Our calculations can be performed on a cluster of machines, allowing us to check protocols for large numbers of participants. [ABSTRACT FROM AUTHOR]

We propose a framework in which anonymity protocols are interpreted as particular kinds of channels, and the degree of anonymity provided by the protocol as the converse of the channel's capacity. We also investigate how the adversary can test the system to try to infer the user's identity, and we study how his probability of success depends on the characteristics of the channel. We then illustrate how various notions of anonymity can be expressed in this framework, and show the relation with some definitions of probabilistic anonymity in literature. [ABSTRACT FROM AUTHOR]

We describe a type system for the Xdπ calculus, introduced in [8]. An Xdπ-network is a network of locations, where each location consists of both a data tree (which contains scripts and pointers to nodes in trees at different locations) and a process, for modelling process interaction, process migration and interaction between processes and data. Our type system is based on types for locations, trees and processes, expressing security levels. The type system enjoys type preservation under reduction (subject reduction). In consequence of subject reduction we prove the following security properties. In a well-typed Xdπ-network, data in a location are accessible only to processes in locations of equal or higher security level. Moreover, processes originating in a location can only go to locations of equal or less security level, with the exception of movements which are returns to the "source" location. [ABSTRACT FROM AUTHOR]

Remote internet voting incorporates many of the core challenges of trusted global computing. In this paper, we present the Kiezen op Afstand (KOA) system. KOA is a Free Software, remote voting system developed for the Dutch government in 2003/2004. In addition to being Open Source, it is also partially formally specified and verified. This paper summarises the work carried out to date on the KOA system. It charts the evolution of the system, from its initial conception by the Dutch Government, through to its current status. It also describes a roadmap of milestones towards completing its next release: a Free Software, general-purpose, formally specified and verified internet voting system, that incorporates Proof Carrying Code technology for software update and allows trustworthy voting from a mobile phone. We propose that the KOA system should be used as an experimental platform for research in electronic and internet voting; we are not saying that we have solved any of the major problems inherent in voting with computers. [ABSTRACT FROM AUTHOR]

Intuitively, a cache-oblivious algorithm implements an adaptive strategy which runs efficiently on any memory hierarchy without requiring previous knowledge of the parameters of the hierarchy. For this reason, cache-obliviousness is an attractive feature of an algorithm meant for a global computing environment, where software may be run on a variety of different platforms for load management purposes. In this paper we present a negative result on cache-obliviousness, namely, we show that an optimal cache-oblivious algorithm for the fundamental primitive of matrix transposition cannot exist without the tall cache assumption, which forces the (unknown) parameters of the memory hierarchy to satisfy a certain technical relation. Our contribution specializes the result of Brodal and Fagerberg for general permutations to matrix transposition, and provides further evidence that the tall cache assumption is often necessary to attain optimality in the context of cache-oblivious algorithms. [ABSTRACT FROM AUTHOR]

We study a problem of scheduling client requests to servers. Each client has a particular latency requirement at each server and may choose either to be assigned to some server in order to get serviced provided that her latency requirement is met or not to participate in the assignment at all. From a global perspective, in order to optimize the performance of such a system, one would aim to maximize the number of clients that participate in the assignment. However, clients may behave selfishly in the sense that each of them simply aims to participate in an assignment and get serviced by some server where her latency requirement is met with no regard to the overall system performance. We model this selfish behavior as a strategic game, show how to compute equilibria efficiently, and assess the impact of selfishness on system performance. We also show that the problem of optimizing performance is computationally hard to solve, even in a coordinated way, and present efficient approximation and online algorithms. [ABSTRACT FROM AUTHOR]

A central point when integrating services concerns to the description, agreement and enforcement of the quality aspect of service interaction, usually known as Service Level Agreement (SLA). This paper presents a framework for SLA negotiation based on fuzzy sets. We propose (i) a request language for clients to describe quality preferences, (ii) a publication language for providers to define the qualities of their offered services, and (iii) a decision procedure for granting any client request with a SLA contract fitting the requestor requirements. We start with a restricted framework in which the different qualities of a service are handled independently (as being orthogonal) and then we propose an extension that allows clients and providers to express dependencies among different qualities. [ABSTRACT FROM AUTHOR]

Model transformations, like refinement or refactoring, have to respect the semantics of the models transformed. In the case of behavioural models this semantics can be specified by transformations, too, describing an abstract interpreter for the language. Both kinds of transformations, if given in a rule-based way, can formally be described as graph transformations. In this paper, we present executable business processes, their operational semantics and refactoring, as an example of this fact. Using results from graph transformation theory about critical pairs and local confluence, we show that our transformations preserve the semantics of processes. The analysis is performed by means of the graph transformation tool AGG. [ABSTRACT FROM AUTHOR]

We study the problems related to querying large, distributed XML documents. Our proposal takes the form of a new process calculus in which XML data are processes that can be queried by means of concurrent pattern-matching expressions. What we achieve is a functional, strongly-typed programming model based on three main ingredients: an asynchronous process calculus that draws features from π-calculus and concurrent-ML; a model where both documents and expressions are represented as processes, and where evaluation is represented as a parallel composition of the two; a static type system based on regular expression types. [ABSTRACT FROM AUTHOR]

We illustrate the use of recent, non-trivial proof techniques for weak bisimulation by analysing a generic framework for the definition of distributed abstract machines based on a message-passing implementation. The definition of the framework comes from previous works on a specific abstract machine; however, its new presentation, as a parametrised process algebra, makes it suitable for a wider range of calculi. A first version of the framework can be analysed using the standard bisimulation up to expansion proof technique. We show that in a second, optimised version, rather complex behaviours appear, for which more sophisticated techniques, relying on termination arguments, are necessary to establish behavioural equivalence. [ABSTRACT FROM AUTHOR]

We present PRISMA, a parametric calculus that can be instantiated with different interaction policies, defined as synchronization algebras with mobility of names (SAMs). We define both operational semantics and observational semantics of PRISMA, showing that the second one is compositional for any SAM. We give examples based on heterogeneous SAMs, a case study on Fusion Calculus and some simple applications. Finally, we show that basic categorical tools can help to relate and to compose SAMs and PRISMA processes in an elegant way. [ABSTRACT FROM AUTHOR]