Roberto Lucchi

SOCK: a calculus for service oriented computing

Service oriented computing is an emerging paradigm for designing distributed applications where service and composition are the main concepts it is based upon. In this paper we propose SOCK, a three-layered calculus equipped with a formal semantics, for addressing all the basic mechanisms of service communication and composition. The main contribute of our work is the development of a formal framework where the service design is decomposed into three fundamental parts: the behaviour, the declaration and the composition where each part can be designed independently of the other ones.

Choreography and orchestration: a synergic approach for system design

Choreography and orchestration languages deal with business processes design and specification. Referring to Web Services technology, the most credited proposals are WS-CDL about choreography and WS-BPEL about orchestration. A closer look to such a kind of languages highlights two distinct approaches for system representation and management. Choreography describes the system in a top view manner whereas orchestration focuses on single peers description. In this paper we define a notion of conformance between choreography and orchestration which allows to state when an orchestrated system is conformant to a given choreography. Choreography and orchestration are formalized by using two process algebras and conformance takes the form of a bisimulation-like relation.

A Framework for Generic Error Handling in Business Processes

Recently the term Web Services Choreography has been introduced to address some issues related toWeb Services Composition. Several proposals for describing Choreography for Business Processes have been presented in the last years and many of these languages make use of concepts as longrunning transactions and compensations for coping with error handling. BPEL4WS, the most accredited candidate for becoming a standard in Choreography, provides three di.erent mechanisms for coping with abnormal situations: Exception Handling, Event Handling and Compensation Handling. The complexity of BPEL4WS makes it di.cult to formally de.ne this framework, thus limiting the formal reasoning about the designed applications. In this paper we advocate that three di.erent mechanisms for error handling are not necessary and we formalize a novel choreography language, based on the idea of event noti.cation as the only error handling mechanism. We can take advantages of this formal description in two ways. Firstly, this language represents by itself a proposal of simpli.cation for BPEL4WS including an unambiguous speci.cation. Secondly, an implementor of an actual BPEL4WS orchestration engine should implement simply this single mechanism providing all the remaining ones by compilation. Notably, the proposed framework is expressive enough to compare di.erent solutions for managing long running transactions such as BPEL4WS and StAC.

A Formal Framework for Web Services Coordination

Recently the term Web Services Choreography has been introduced to address some issues related to Web Services Composition and Coordination. Several proposals for describing Choreography for Business Processes have been presented in the last years and many of these languages (e.g. BPEL4WS) make use of concepts as long-running transactions and compensations for coping with error handling. However, the complexity of BPEL4WS makes it difficult to formally define this framework, thus limiting the formal reasoning about the designed applications. In this paper, we formally address Web Services Coordination with particular attention to Web transactions. We enhance our past work - the Event Calculus - introducing two main novelties: i) a multicast event notification mechanism, and ii) event scope names binding. The former enables an easier specification of complex coordination scenarios - such as E-commerce applications require - while the latter allows many new interesting behaviors which can be very useful in business scenarios: the introduction of private event scope names - used to deal with security and privacy - and a dynamic event scopes definition that can be used to manage multiple instances of the same application.

WSSecSpaces: a secure data-driven coordination service for Web Services applications

Web Services standards and protocols (WSDL, UDDI, SOAP, etc.) are the basis of a novel technology supporting Web based applications. Web Services are components offering ports at which service invocations can be sent using XML-based protocols. The tools currently proposed for specifying and programming the interdependencies among Web Services (BPEL, BizTalk, etc.) support the description of the flow of service invocation needed among collaborating Web Services in order to complete a specific task. In this paper we discuss the design and the implementation of a higher-level interaction model for Web Services that follows the tradition of data-driven coordination: Web Services do not coordinate via direct service invocation, but their interaction is mediated by a coordination space where shared data are stored and retrieved. Moreover, our proposal extends the traditional data-driven coordination model with a more sophisticated pattern matching mechanism that supports a controlled access to the shared data.

Quantitative information in the tuple space coordination model

Tuple Spaces is a well-known coordination model at the basis of coordination languages such as Linda, JavaSpaces and TSpaces. Tuple spaces are flat and unstructured multisets of tuples that can be accessed via output, read, and input operations. We investigate, from an expressiveness viewpoint, the impact of the introduction of quantitative information in the tuple space coordination model in order to quantify the relevance or importance of each tuple. We consider two possible interpretations for this information: in the first case it quantifies a weight indicating how much frequently each tuple should be retrieved, in the second case it expresses a priority level for the tuples.

Reasoning about interaction patterns in choreography

Choreography languages provide a top-view design way for describing complex systems composed of services distributed over the network. The basic building block of such languages is the interaction between two peers which are of two kinds: request and request-respond. WS-CDL, which is the most representative choreography language, supports a pattern for programming the request interaction and two patterns for the request-respond one. Furthermore, it allows to specify if an interaction is aligned or not whose meaning is related to the possibility to control when the interaction completes. In this paper we reason about interaction patterns by analyzing their adequacy when considering the fact that they have to support the alignment property. We show the inadequacy of the two patterns supporting the request-respond interaction; one of them because it does not permit to reason on alignment at the right granularity level and the other one for some expressiveness lacks.

Web Services for E-commerce: guaranteeing security access and quality of service

Being E-commerce one of the most critical Internet application, it is fundamental to employ technologies which guarantee not only secure transactions but also an adequate quality of service. In this paper we present a solution to this problem based on an extension of the emerging Web Service technology. In particular we introduce a new Web Service discovery protocol that extends standard UDDI capability by addiing: (i) the discovery of Web Services at run-time supporting environment re-configurations, (ii) security access control to Web Services and (iii) a mechanism for distributing service invocations among several Web Services implementing (at different efficiency levels) the same task. Discovery at run-time is realized by dynamically resorting to the discovery protocol (a Web Service itself) every time a service is invoked, access control is obtained by employing symmetric and asymmetric keys, while the different efficiency levels of service implementations are represented via weights. The proposal is formalized by employing a coordination platform, which is a probabilistic extension of the existing WSSecSpaces. Such a platform is based on a data space, where data can be not only protected via access control mechanisms, like in WSSecSpaces, but also accessed probabilistically.

Supporting e-commerce systems formalization with choreography languages

E-commerce as well as B2B applications are essentially based on interactions between different people and organizations (e.g. industry, banks, customers) that usually exploit the Internet as communication media. Web Services provide a mean to deal with these aspects. In this paper we show, via a case study, how choreography and orchestration languages allow us to express behaviour policies between the involved entities (interactions modalities, interdependencies, security requirements); in particular we consider that they can be used not only for describing behavioural rules but also for designing and testing whether the involved entities move according with system specifications.

SENSORIA process calculi for service-oriented computing

The IST-FET Integrated Project SENSORIA aims at developing a novel comprehensive approach to the engineering of service-oriented software systems where foundational theories, techniques and methods are fully integrated in a pragmatic software engineering approach. Process calculi and logical methods serve as the main mathematical basis of the SENSORIA approach. In this paper we give first a short overview of SENSORIA and then focus on process calculi for service-oriented computing. The Service Centered Calculus SCC is a general purpose calculus which enriches traditional process calculi with an explicit notion of session; the Service Oriented Computing Kernel SOCK is inspired by the Web services protocol stack and consists of three layers for service description, service engines, and the service network; Performance Evaluation Process Algebra (PEPA) is an expressive formal language for modelling distributed systems which we use for quantitative analysis of services. The calculi and the analysis techniques are illustrated by a case study in the area of distributed e-learning systems.