Section: New Results

Service-oriented computing

Participants : Mila Dalla Preda, Ornela Dardha, Maurizio Gabbrielli, Elena Giachino, Claudio Guidi, Jacopo Mauro, Fabrizio Montesi, Davide Sangiorgi.

Primitives

In the context of Service-Oriented Architectures (SOAs), the integration of services is an important aspect that is usually addressed by using specific tools, such as Enterprise Service Bus (ESB). Although widely used these ad-hoc solutions do not exploit the possibility of using a mechanism of interface extension to foster the rapid prototyping and deployment of in-the-middle entities that compose services abstracting from the order in which they exchange messages. We have proposed [29] a framework to perform service integration, based on the extension of service interfaces, capturing a class of service integrators that are decoupled from the services they integrate in an SOA. We also provide a reference implementation for the primitive of service integration by extending the Jolie language, thus allowing for the experimentation with real SOA scenarios. We have shown [30] how our methodology differs from the standard practice with ESB.

Contracts and sessions

Contracts are descriptions of the functionalities offered by a component or a service, and of the way these functionalities may be accessed by clients. A contract may include a description of the component capabilities, place constraints on their usage, as well as declare preferences, entitlements and credentials. When a client wants to use one of the functionalities offered, it engages a dialogue (e.g., a sequence of interactions) with the servers; this is usually called a session.

Contracts specify the expected dialogue in a session and they can be expressed as types, usually called session types in this context.

A session type describes communication by specifying type and direction of data exchanged between two parties. When session types and session primitives are added to the syntax of the types and terms of a language, they give rise to additional separate syntactic categories. As a consequence, there may be duplication of efforts in the theory: the proofs of properties must be checked both on ordinary types and on session types. We have shown [32] that this duplication is not necessary, by exhibiting an encoding of (dyadic) session types into ordinary types. Using the encoding, the properties of session types are derived as straightforward corollaries.

We have also studied the problem of handling unexpected or unwanted conditions in sessions, that may change the default execution of distributed communication protocols. We have proposed [14] a global escape mechanism; it can handle such events while preserving compatibility of multiparty conversations. This flexibility enables us to model complex exceptions such as criss-crossing global interactions and error handling for distributed cooperating threads. Guided by multiparty session types, our semantics is proven to provide a termination algorithm for global escapes, as well as further safety properties, such as progress within the session and atomicity of escapes with respect to the subset of involved participants.