Policy-Protocol Interaction in Composite Processes
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Message policy is defined to be the description of the disposition of messages of a single type, when received by a group of processes. Group policy applies to all the processes of a group, but for a single message type. It is proposed that group policy be specified in an expression which is separate from the code of the processes of the group, and in a separate notation. As a result, it is possible to write policy expressions which are independent of process state variables, and as well use a simpler control notation based on regular expressions. Input protocol, on the other hand, applies to single processes or a group as a whole for all message types. Encapsulation of processes is presented with an unusual emphasis on the transactions and resources which associate with an encapsulated process rather than the state space of the process environment. This is due to the notion of encapsulation without shared variables, and to the association between group policies, message sequences and transactions.