Procol: a protocol-constrained concurrent object-oriented language

PROCOL is a simple concurrent object-oriented language supporting a distributed, incremental and dynamic object environment. Its communication is based on unidirectional messages. Objects are only bound during actual message transfer and not during the processing of the message. This short-duration object binding promotes parallelism. In communications both client and server have to be specified, either by object instance identifiers, or by type. Therefore client-server mappings may be 1−1, n−1, or 1− n, though only one message is transffered. A novel feature of PROCOL is explicit access control: communication is subject to a protocol defined for each object. This protocol is a specification of the occurrence and sequencing of the interaction between the object and its communication partners. The use of such protocols fosters structured, safer and potentially verifiable communication between objects.