Alessandro Lapadula

SENSORIA Patterns: Augmenting Service Engineering with Formal Analysis, Transformation and Dynamicity

The IST-FET Integrated Project Sensoria is developing a novel comprehensive approach to the engineering of service-oriented software systems where foundational theories, techniques and methods are fully integrated into pragmatic software engineering processes. The techniques and tools of Sensoria encompass the whole software development cycle, from business and architectural design, to quantitative and qualitative analysis of system properties, and to transformation and code generation. The Sensoria approach takes also into account reconfiguration of service-oriented architectures (SOAs) and re-engineering of legacy systems.

A calculus for orchestration of web services

We introduce COWS (Calculus for Orchestration of Web Services), a new foundational language for SOC whose design has been influenced by WS-BPEL, the de facto standard language for orchestration of web services. COWS combines in an original way a number of ingredients borrowed from well-known process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting different fromany of them. Several examples illustrates COWS peculiarities and show its expressiveness both for modelling imperative and orchestration constructs, e.g. web services, flow graphs, fault and compensation handlers, and for encoding other process and orchestration languages.

A model checking approach for verifying COWS specifications

We introduce a logical verification framework for checking functional properties of service-oriented applications formally specified using the service specification language COWS. The properties are described by means of SocL, a logic specifically designed to capture peculiar aspects of services. Service behaviours are abstracted in terms of Doubly Labelled Transition Systems, which are used as the interpretation domain for SocL formulae. We also illustrate the SocL model checker at work on a bank service scenario specified in COWS.

A formal account of WS-BPEL

We introduce Blite, a lightweight language for web services orchestration designed around some of WS-BPEL peculiar features like partner links, process termination, message correlation, long-running business transactions and compensation handlers. Blite formal presentation helps clarifying some ambiguous aspects of the WS-BPEL specification, which have led to engines implementing different semantics and, thus, have undermined portability of WS-BPEL programs over different platforms. We illustrate the main features of Blite by means of many examples, some of which are also exploited to test and compare the behaviour of three of the most known free WS-BPEL engines.

A logical verification methodology for service-oriented computing

We introduce a logical verification methodology for checking behavioral properties of service-oriented computing systems. Service properties are described by means of SocL, a branching-time temporal logic that we have specifically designed for expressing in an effective way distinctive aspects of services, such as, acceptance of a request, provision of a response, correlation among service requests and responses, etc. Our approach allows service properties to be expressed in such a way that they can be independent of service domains and specifications. We show an instantiation of our general methodology that uses the formal language COWS to conveniently specify services and the expressly developed software tool CMC to assist the user in the task of verifying SocL formulas over service specifications. We demonstrate the feasibility and effectiveness of our methodology by means of the specification and analysis of a case study in the automotive domain.

Regulating data exchange in service oriented applications

We define a type system for COWS, a formalism for specifying and combining services, while modelling their dynamic behaviour. Our types permit to express policies constraining data exchanges in terms of sets of service partner names attachable to each single datum. Service programmers explicitly write only the annotations necessary to specify the wanted policies for communicable data, while a type inference system (statically) derives the minimal additional annotations that ensure consistency of services initial configuration. Then, the language dynamic semantics only performs very simple checks to authorize or block communication. We prove that the type system and the operational semantics are sound. As a consequence, we have the following data protection property: services always comply with the policies regulating the exchange of data among interacting services. We illustrate our approach through a simplified but realistic scenario for a service-based electronic marketplace.

AGILE: Software Architecture for Mobility.

Architecture-based approaches have been promoted as a means of controlling the complexity of system construction and evolution, in particular for providing systems with the agility required to operate in turbulent environments and to adapt very quickly to changes in the enterprise world. Recent technological advances in communication and distribution have made mobility an additional factor of complexity, one for which current architectural concepts and techniques can be hardly used. The AGILE project is developing an architectural approach in which mobility aspects can be modelled explicitly and mapped on the distribution and communication topology made available at physical levels. The whole approach is developed over a uniform mathematical framework based on graph-oriented techniques that support sound methodological principles, formal analysis, and refinement. This paper describes the AGILE project and some of the results gained during the first project year.

Using formal methods to develop WS-BPEL applications

In recent years, WS-BPEL has become a de facto standard language for the orchestration of Web services. However, there are still some well-known difficulties that make programming in WS-BPEL a tricky task. In this paper, we first point out major loose points of the WS-BPEL specification by means of many examples, some of which are also exploited to test and compare the behaviour of three of the best-known freely available WS-BPEL engines. We show that, in fact, these engines implement different semantics, which undermines the portability of WS-BPEL programs over different platforms. Then we introduce Blite, a prototypical orchestration language equipped with a formal operational semantics, which is closely inspired by, but simpler than, WS-BPEL. Indeed, Blite is designed around some of WS-BPELs distinctive features such as partner links, process termination, message correlation, long-running business transactions, and compensation handlers. Finally, we present BliteC, a software tool supporting a rapid and easy development of WS-BPEL applications via the translation of service orchestrations written in Blite into executable WS-BPEL programs. We illustrate our approach by means of a running example borrowed from the official specification of WS-BPEL.

COWS: a timed service-oriented calculus

COWS (Calculus for Orchestration of Web Services) is a foundational language for Service Oriented Computing that combines in an original way a number of ingredients borrowed from well-known process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting different from any of them. In this paper, we extend COWS with timed orchestration constructs, this way we obtain a language capable of completely formalizing the semantics of WS-BPEL, the ‘de facto’ standard language for orchestration of web services. We present the semantics of the extended language and illustrate its peculiarities and expressiveness by means of several examples.COWS (Calculus for Orchestration of Web Services) is a foundational language for Service Oriented Computing that combines in an original way a number of ingredients borrowed from well-known process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting different from any of them. In this paper, we extend COWS with timed orchestration constructs, this way we obtain a language capable of completely formalizing the semantics of WS-BPEL, the ‘de facto’ standard language for orchestration of web services. We present the semantics of the extended language and illustrate its peculiarities and expressiveness by means of several examples.

Service Discovery and Negotiation With COWS

To provide formal foundations to current (web) services technologies, we put forward using COWS, a process calculus for specifying, combining and analysing services, as a uniform formalism for modelling all the relevant phases of the life cycle of service-oriented applications, such as publication, discovery, negotiation, deployment and execution. In this paper, we show that constraints and operations on them can be smoothly incorporated in COWS, and propose a disciplined way to model multisets of constraints and to manipulate them through appropriate interaction protocols. Therefore, we demonstrate that also QoS requirement specifications and SLA achievements, and the phases of dynamic service discovery and negotiation can be comfortably modelled in COWS. We illustrate our approach through a scenario for a service-based web hosting provider.