TEPC, its object resource model, operations and service behaviour An assumed and simplified object behaviour of TEPC is shown in the state dia- gram in Fig. 6.25. The diagram shows a scenario where the TECA originates the behaviour by requesting that the teleservice X be established between the two ter- minal systems. To keep the diagram reasonably simple, it is assumed that no tele- service resource is needed. Note that when the service relations to TECA and TECE were set up, TEPC relates the corresponding TE-SAPIs (A and E) to these relations. This access procedure is implied (part of the corresponding abstract net- work), and therefore not part of the state diagram. A state diagram for an object can give the complete picture of the behaviour, if all pre-and postconditions are exactly specified. AML also offers a syntax for expressing conditions as logical expressions (predicates) over a data model (called state vector) of a resource model. Normally, however, such expressions are intro- duced first if the behaviour description is to be used in simulation, code generation or formal verifications processes. A more human-friendly method is to provide a verbal description that describes how the object is using and modifying the object resource model for each transition. The description that follows Fig. 6.25 describes the state diagram in that way. 6 Process Control System Modelling AnotInCall A-servReq(crA,x,E) A-servReq(crA,x,E) pre: problems pre: noProblems post: A-servRef(crE,...) E-servRej(crE) E-servinv(crE,x,A) A-servRef(crA,...) AnotInCall Epending1 A-servIntOrd(crA) E-servReq(crA) Epending2 post: E-servRej(crE) E-servReq(crA) CNPC-conReq(conld15,CNU1,CNU5) E-servRef(...) AnotInCall CNPC-conRef(conId15) conPending A-servRef(...) CNPC-conCnf(conld15,{CNU1,B1}) AnotInCall B-servRef(...) post: A-servCnf(crA,B1) A-userServRel(crA) E-servCnf(crE) CNPC-userConRelOrd(conld15 E-nwServRel(crE) AnotInCall AandEinCall E-userServRel(crE) CNPC-nwConRelRepCnf(conld15) CNPC-userConRelOrd(conld15 A-nwServRel(crA) A-nwServR