ted SO that the service name that is placed inside the unit symbol shows that the unit uses the service. If the service name is placed out- side the unit symbol, it shows that the unit provides the service, and therefore must realize it. 9 A primitive service is defined by a set of operations that are related through a common data set (like an "object"). The primitive service concept is discussed in Chap. 7. 3.2 The Communication Service Provider 3.2.5 Service Access Point Operations In general, the ASPs that can be defined for any kind of interface in an AML model are specified by the modeller to specify. AML provides a syntax for operations and ASPs for that purpose, and a classification system for operations, called the AML operation classification system. Details of the system are found in Sect. 7.4.4. This system defines which types of ASPs (primitive type10) can exist for six different operation classes ¹ 1. The system allows to define which party in an interface decides on the execution of a referred operation, if the operation gives a response, and, if so, which are the positive and negative responses. An ASP refers to an oper- ation. It defines one out of ten possible primitive types, and it provides a set of parameters. There can exist between 1 and 5 ASPs associated with an operation. Figure 3.25 gives an example of a type of receive operation specified by using this system. The operation class REQUEST defines three primitive types: Request, Confirm and Refuse. Operation name is: srecCon Operation class is: REQUEST Operation annotation in models is: srecConREQ Abstract service primitives, Abstract service primitives, long form short form srecConRequest(CEI) srecConReq(CEI) srecConConfirm(SDU) srecConCnf(SDU) srecConRefuse(Cause{...}) srecConRef(Cause(...)} Fig. 3.25 An operation example To facilitate modelling, AML provides, in some cases, predefined operations and ASPs that can be modified or replaced by the modeller. We call them generic operations and generic ASPs. For interfaces that refer to gener