View article

ShaDe is an object-based coordination language. It offers a basic abstraction called the Object Space, that is similar to a tuple space with the difference that it contains objects and messages. ShaDe objects are active, ie they are units (places) of computation. Each object encapsulates a state in form of multiset of tuples and methods in form of rewriting rules. The object space is a coordination medium supporting a number of inter-object associative communication mechanisms, namely unicast, multicast, and broadcast. The most interesting feature of Shade is that coordination is expressed by rules. We exploit such a feature to build" coordination" services enacting declarative cooperation laws. We demonstrate the use of the language building two coordination applications, namely a distributed auction system and a stock exchange system.