() pending state Mahatma-timeCnf({12}) Fig. 7.24 The communication event A communication event consists of values of four syntactical elements: service relation prefix, operation name, primitive type and parameter set. 7.4 Elements of Interactions The service relation prefix (two possible forms): in the state diagram the prefix identifies the other party by name or identifier. In Fig. 7.24, Thomas, Nelson and Mahatma are such names. Note that the prefixes of the same event are dif- ferent on the initiating and the detecting side. Another possibility is to annotate service relations in the service network with service relation identifiers (SRid), which implies that the same prefix can be used on both the initiating and the detecting side. To handle a service relation prefix that allows dialogues to be maintained between service objects, is part of the general functionality of abstract protocols, see Sect. 7.7.2. It is only necessary to use service relation prefixes when communication events are detached from the service network model, as in state diagrams and in abstract networks. The operation name: in Fig. 7.24, time is the only operation name that occurs. An operation name must have a primitive service identifier (PSid) prefix if the operation name is not unique in the sysnet that is modelled. Assume, e.g. that you are modelling a complex sysnet, comprising several OSI layers. The OSI model uses the operation name connect in all its network service interfaces. Since creating an (OSI) )presentation layer connection is definitely an operation other than creating a link connection, the complete operation names are, in this case, DL/connect and P/connect, where DL and P are primitive service names, though OSI calls them (layer)initials. Use of primitive service names as prefixes to operation names is an important consideration in modelling complex sysnets, since there are many operations to name. Good operation names can and should be reused, although they may refer to completely different operations. The primitive