Colloquium Computing Science



Date:                            Monday,  28 January 2008      

Speaker:                      Farhad Arbab

                                    CWI, Amsterdam and LIACS, Leiden University         

Room and time:           5161.0267 (Bernoulliborg), 16.00



Title:    Third-Party Coordination of Distributed Services





Different aspects of coordination in Service Oriented Computing (SoC) have been

considered as separate, complementary (if not competing) concerns, such as

choreography and orchestration.  Work on proposals and standards to deal with

these concerns is still on-going; however, the results appear as ad-hoc

(albeit useful) collections of ideas and constructs that convey no systematic

conceptual model or formal theoretical foundation.  We believe a coherent approach

to deal with various aspects of coordination must consider all coordination concerns

as an integrated whole, and as an issue inseparable from the context of composition

(of services).  Reo offers precisely such a model.


Reo is an exogenous coordination language based on a calculus of channel composition.

In Reo, services are composed using complex coordinators, called connectors, that

in turn are compositionally built out of simpler ones.The simplest connectors in Reo

are a set of mobile channels with well-defined behavior supplied by users. Reo supports

third-party composition and coordination of services: each connector in Reo imposes

a specific coordination pattern on the I/O operations performed by the services that it

interconnects, without the knowledge of those services.  Alternative formal semantics

for Reo exist, e.g., based on stream calculus and constraint automata. Channel

composition in Reo is a surprisingly powerful mechanism for construction of connectors.

We demonstrate the expressive power of connector composition in Reo through

a number of examples. 




Colloquiumcoördinator is Prof.dr. M. Aiello, Dr. M. Biehl (e-mail: