Common use of Protocol Description Clause in Contracts

Protocol Description. Another difference to existing work is how we describe the protocol; we do not use UML sequence diagrams to describe the protocol as they often cannot capture the entire set of message exchanges possible in the network environment described above. To describe the behaviour of each re-negotiation participant we provide a finite state machine to describe the state of the contract, similar to the WS- Agreement specification. However, unlike in WS-Agreement, the state machine is not shared between the negotiation participants. Instead each participant has their own ‘copy’ of the state machine which they update as they send and receive messages. In addition, we also explain the possible messaging events using pre- and post-constraints that together specify the conditions which must be satisfied before and after each message is sent. The conditions explain each messaging event as an atomic action and together describe the messaging behaviour of each participant in the re-negotiation protocol.