Behavioural theory at work: program transformations in a service-centred calculus (original) (raw)

From Architectural to Behavioural Specification of Services

Electronic Notes in Theoretical Computer Science, 2009

Many efforts are currently devoted to provide software developers with methods and techniques that can endow service-oriented computing with systematic and accountable engineering practices. To this purpose, a number of languages and calculi have been proposed within the S project that address different levels of abstraction of the software engineering process. Here, we report on two such languages and the way they can be formally related within an integrated approach that can lead to verifiable development of service components from more abstract architectural models of business activities.

Describing and reasoning on Web Services using Process Algebra

International Journal of Business Process Integration and Management, 2006

We argue that essential facets of web services, and especially those useful to understand their interaction, are best described using process-algebraic notations. Web service description and execution languages such as BPEL are essentially process description languages; they are based on primitives for behaviour description and message exchange which can also be found in more abstract languages such as process algebras. One legitimate question is therefore whether the web services community can benefit from the sophisticated languages and tools developed in the process algebra area. Our investigations suggest a positive answer, and we claim that process algebras provide solutions to a number of challenges raised by the web services paradigm, among which are central issues of orchestration and choreography. We show on a case study that readily available tools based on process algebra are effective at verifying that compositions of services obtained by choreography and orchestration conform their requirements and respect properties. We suggest a general framework based on a mapping between process algebra and web services written in BPEL, and illustrate both the modelling of services by process algebra and the use of reasoning tools.

MarCaSPiS: a Markovian Extension of a Calculus for Services

Electronic Notes in Theoretical Computer Science, 2009

Service Oriented Computing (SOC) is a design paradigm that has evolved from earlier paradigms including object-orientation and component-based software engineering. Important features of services are compositionality, context-independence, encapsulation and re-usability. To support the formal design and analysis of SOC applications recently a number of Service Oriented Calculi have been proposed. Most of them are based on process algebras enriched with primitives specific of service orientation such as operators for manipulating semi-structured data, mechanisms for describing safe client-service interactions, constructors for composing possibly unreliable services and techniques for services query and discovery. In this paper we show a versatile technique for the definition of Structural Operational Semantics of MarCaSPiS, a Markovian extension of one of such calculi, namely the Calculus of Sessions and Pipelines, CaSPiS. The semantics deals in an elegant way with a stochastic version of two-party synchronisation, typical of a service-oriented approach, and with the problem of transition multiplicity while preserving highly desirable mathematical properties such as associativity and commutativity of parallel composition. We also show how the proposed semantics can be naturally used for defining a bisimulation-based behavioural equivalence for MarCaSPiS terms that induces the same equalities as those obtained via Strong Markovian Equivalence.

A formal model for service-oriented interactions

Science of Computer Programming, 2012

In this paper, we provide a mathematical semantics for a fragment of a language -SRML-that we have defined in the IST-FET-GC2 Integrated Project SENSORIA for modelling service-oriented systems. The main goal of this research is to make available a foundational basis for the development of practical modelling languages and tools that designers can use to model complex services at a level of abstraction that captures business functionality independently of the languages in which services are implemented and the platforms in which they execute. The basic artefact of the language is the service module, which provides a model for a complex service in terms of a number of components that jointly orchestrate a business function and may dynamically discover and bind to external parties that can deliver required functionalities. We define a mathematical model of computation and an associated logic for service-oriented systems based on the typical business conversations that occur between the parties that deliver a service. We then define the semantics of SRML service modules over this model and logic, and formulate a property of correctness that guarantees that services programmed and assembled as specified in a module provide the business functionality advertised by that module. Finally, we define an algebraic operation of composition of service modules that preserves correctness. To the best of our knowledge, there is no other formal approach that has been defined from first principles with the aim of capturing the business nature of service conversations and support service assembly based on the business logic that is required, not as it is programmed.

Structured Formalization of Service-Oriented Specifications

2009 16th Annual IEEE International Conference and Workshop on the Engineering of Computer Based Systems, 2009

We present and formalize concepts for the structured specification of system behavior based on services. Services are patterns of interaction between reactive components, thus supporting especially the development of distributed systems. We introduce a core set of concepts for the specification of basic services as well as for the combination of those to complex functionality. The result is an expressive mechanism for structured behavioral specifications. While basically independent from specific notations, we demonstrate the application of those concepts using (High-level) Message Sequence Charts and Mode Diagrams for the specification of services and their combination. We illustrate the approach using a simple telephone system as a running example.

SCC: A Service Centered Calculus

2006

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.

A symbolic semantics for a calculus for service-oriented computing

2009

We introduce a symbolic characterisation of the operational semantics of COWS, a formal language for specifying and combining service-oriented applications, while modelling their dynamic behaviour. This alternative semantics avoids infinite representations of COWS terms due to the value-passing nature of communication in COWS and is more amenable for automatic manipulation by analytical tools, such as e.g. equivalence and model checkers. We illustrate our approach through a 'translation service' scenario.

From Behavioural Contracts to Session Types

Models, Languages, and Tools for Concurrent and Distributed Programming

We present a research trajectory of the authors and colleagues dealing with the correctness and meaningful composition of software components, trajectory that incrementally traverses successive paradigms and approaches: open distributed processing, contract based reasoning, behavioural typing and session types. This research is grounded on the foundational work of Robin Milner on processes and observation equivalence, and the followup work by De Nicola and Hennessy on testing relations. Indeed, these initial works have set benchmarks that define the meaning of behaviour, which has fostered a full body of research in concurrency and verification. Behavioural typing is one of the avenues opened by these early contributions. This paper is a brief and staged report of the research accomplished by the authors and colleagues, presented in chronological order, starting with their work on the computational model of open distributed processing and ending at their latest work on sessions for web services.

A novel specification and composition language for services

Service-Oriented Architecture (SOA) has emerged as a prominent design style that enables an IT infrastructure to allow different applications to participate in business processes, regardless of their underlying features, by encapsulating them as platform-independent entities that become available via a certain network, primarily the Internet. In order to effectively discover and use the most suitable services, service description should provide a complete behavior model, describing the inputs and preconditions that are required before execution, as well as the outputs and effects of a successful execution. Such service specifications are indispensable in a variety of activities, such as conformance and verification checks, adaptation evaluation and deducing composability of services. Service specifications rely on the expression of conditions that should hold before and after service execution. Such specifications are prone to a family of problems, known in the AI literature as the frame, ramification and qualification problems. These problems deal with the succinct and flexible representation of non-effects, indirect effects and preconditions, respectively. Research in services has largely ignored these problems, at the same time ignoring their effects, such as compromising the integrity and correctness of services and service compositions and the inability to provide justification for unexpected execution results. To address these issues, this thesis proposes the Web Service Specification Language (WSSL), a novel, semantics-aware language for the specification and composition of services, independent of service design models. WSSL's foundation is the fluent calculus, a specification language for robots that offers solutions to the frame, ramification and qualification problems. Further language extensions achieve three major goals: realize service composition via planning, supporting non-deterministic constructs, such as conditionals and loops; include specification of QoS profiles; and support partially observable service states. To investigate WSSL's applicability and demonstrate its benefits, we analyze correctness of the composition extension, decidability and complexity of the underlying theory, as well as compatibility with other related languages in service science. Moreover, an innovative service composition and verification framework is implemented, that advances state-of-the-art by satisfying several desirable requirements simultaneously: ramifications and partial observability in service and goal modeling; non-determinism in composition schemas; dynamic binding of tasks to concrete services; explanations for unexpected behavior; QoS-awareness through pruning and ranking techniques based on heuristics and task-specific goals and an all-encompassing QoS aggregation method for global goals. Experimental evaluation is performed using synthetically generated specifications and composition goals, investigating performance scalability in terms of execution time, as well as optimality with regard to the produced composite process. The results show that, even in the presence of ramifications in some specifications, functional planning is efficient for repositories up to 500 specifications. Also, the cost of functional discovery per single service is insignificant, hence achieving good performance even when executed for multiple candidate plans. Finally, optimality relies mainly on defining suitable problem-specific heuristics; thus, its success depends mostly on the expertise of the composition designer.

Specifying and Composing Interaction Protocols for Service-Oriented System Modelling

Formal Techniques for Networked and Distributed Systems, 2007

We present and discuss a formal, high-level approach to the specification and composition of interaction protocols for service-oriented systems. This work is being developed within the SENSORIA project as part of a language and formal framework supporting the modelling of complex services at the business level, i.e. independent of the underlying platform and the languages in which services are programmed and deployed. Our approach is based on a novel language and logic of interactions, and a mathematical semantics of composition based on graphs. We illustrate our approach using a case study provided by Telecom Italia, one of our industrial partners in the project.