Antonio Brogi

A formal approach to component adaptation

Component adaptation is widelyrecognised to be one of the crucial problems in Component-Based Software Engineering (CBSE). We present a formal methodologyfor adapting components with mismatching interaction behaviour. The three main ingredients of the methodologyare: (1) the inclusion of behaviour specifications in component interfaces, (2) a simple, high-level notation for expressing adaptor specifications, and (3) a fullyautomated procedure to derive concrete adaptors from given high-level specifications.

Formalizing Web Service Choreographies

Current Web service choreography proposals, such as BPEL4WS, BPSS, WSFL, WSCDL or WSCI, provide notations for describing the message flows in Web service collaborations. However, such proposals remain at the descriptive level, without providing any kind of reasoning mechanisms or tool support for checking the compatibility of Web services based on the proposed notations. In this paper we present the formalization of one of these Web service choreography proposals (WSCI), and discuss the benefits that can be obtained by such formalization. In particular, we show how to check whether two or more Web services are compatible to interoperate or not, and, if not, whether the specification of adaptors that mediate between them can be automatically generated ---hence enabling the communication of (a priori) incompatible Web services.

The concurrent language, Shared Prolog

Shared Prolog is a new concurrent logic language. A Shared Prolog system is composed of a set of parallel agents that are Prolog programs extended by a guard mechanism. The programmer controls the granularity of parallelism, coordinating communication and synchronization of the agents via a centralized data structure. The communication mechanism is inherited from the blackboard model of problem solving. Intuitively, the granularity of the logic processes to be elaborated in parallel is large, while the resources shared on the blackboard can be very fined grained. An operational semantics for Shared Prolog is given in terms of a distributed model. Through an abstract notion of computation, the kinds of parallelism supported by the language, as well as properties of infinite computations, such as local deadlocks, are studied. The expressiveness of the language is shown with respect to the specification of two classes of applications: metaprogramming and blackboard systems.

Evolving Logic Programs

Logic programming has often been considered less than adequate for modelling the dynamics of knowledge changing over time. In this paper we describe a simple though quite powerful approach to modelling the updates of knowledge bases expressed by generalized logic programs, by means of a new language, hereby christened EVOLP (after EVOlving Logic Programs). The approach was first sparked by a critical analysis of previous efforts and results in this direction [1,2,7,11], and aims to provide a simpler, and at once more general, formulation of logic program updating, which runs closer to traditional logic programming (LP) doctrine. From the syntactical point of view, evolving programs are just generalized logic programs (i.e. normal LPs plus default negation also in rule heads), extended with (possibly nested) assertions, whether in heads or bodies of rules. From the semantics viewpoint, a model-theoretic characterization is offered of the possible evolutions of such programs. These evolutions arise both from self (or internal) updating, and from external updating too, originating in the environment. This formulation sets evolving programs on a firm basis in which to express, implement, and reason about dynamic knowledge bases, and opens up a number of interesting research topics that we brush on.

Towards an engineering approach to component adaptation

Component adaptation needs to be taken into account when developing trustworthy systems, where the properties of component assemblies have to be reliably obtained from the properties of its constituent components. Thus, a more systematic approach to component adaptation is required when building trustworthy systems. In this paper, we illustrate how (design and architectural) patterns can be used to achieve component adaptation and thus serve as the basis for such an approach. The paper proposes an adaptation model which is built upon a classification of component mismatches, and identifies a number of patterns to be used for eliminating them. We conclude by outlining an engineering approach to component adaptation that relies on the use of patterns and provides additional support for the development of trustworthy component-based systems.

Semantics-based composition-oriented discovery of Web services

Service discovery and service aggregation are two crucial issues in the emerging area of service-oriented computing (SOC). We propose a new technique for the discovery of (Web) services that accounts for the need of composing several services to satisfy a client query. The proposed algorithm makes use of OWL-S ontologies, and explicitly returns the sequence of atomic process invocations that the client must perform in order to achieve the desired result. When no full match is possible, the algorithm features a flexible matching by returning partial matches and by suggesting additional inputs that would produce a full match.

Modular logic programming

Modularity is a key issue in the design of modern programming languages. When designing modular features for declarative languages in general, and for logic programming languages in particular, the challenge lies in avoiding the superimposition of a complex syntactic and semantic structure over the simple structure of the basic language. The modular framework defined here for logic programming consists of a small number of operations over modules which are (meta-) logically defined and semantically justified in terms of the basic logic programming semantics. The operations enjoy a number of algebraic properties, thus yielding an algebra of modules. Despite its simplicity, the suite of operations is shown capable of capturing the core features of modularization: information hiding, import/export relationships, and construction of module hierarchies. A metalevel implementation and a compilation-oriented implementation of the operations are provided and proved sound with respect to the semantics. The compilation-oriented implementation is based on manipulation of name spaces and provides the basis for an efficient implementation.

The Refined Extension Principle for Semantics of Dynamic Logic Programming

Over recent years, various semantics have been proposed for dealing with updates in the setting of logic programs. The availability of different semantics naturally raises the question of which are most adequate to model updates. A systematic approach to face this question is to identify general principles against which such semantics could be evaluated. In this paper we motivate and introduce a new such principle the refined extension principle. Such principle is complied with by the stable model semantics for (single) logic programs. It turns out that none of the existing semantics for logic program updates, even though generalisations of the stable model semantics, comply with this principle. For this reason, we define a refinement of the dynamic stable model semantics for Dynamic Logic Programs that complies with the principle.

Composition-Oriented service discovery

Service discovery and service aggregation are two crucial issues in the emerging area of Service-oriented Computing (SoC). We propose a new technique for the discovery of (Web) services that accounts for the need of composing several services to satisfy a client query. The proposed algorithm makes use of OWL-S ontologies, and explicitly returns the sequence of atomic process invocations that the client must perform in order to achieve the desired result. When no full match is possible, the algorithm features a flexible matching by returning partial matches and by suggesting additional inputs that would produce a full match.

Behaviour-Aware Discovery of Web Service Compositions

A major challenge for service-oriented computing is how to discover and compose (Web) services to build complex applications. We present a matchmaking system that exploits both semantics and behavioural information to discover service compositions capable of satisfying a client request.