the object to which a service rela- tion is wanted, by either a primitive service identifier (PSid) or by an object identifier (OBid). If a PSid is used, the OBH will always instantiate a new serv- ice object that can handle the referred primitive service. If OBid is used, it is a reference to an existing object (like the object reference in CORBA). How the requesting abstract machine acquires this identifier is outside the scope of the OBH service. Obviously, it requires that all service objects that can be accessed this way must be registered in some database that provides some type of naming service. The Confirm event of seizeServRel considers the possibility that some service relations can be established, others cannot. The reason for not accepting service relations might be that the referred object is busy and multiple access is not allowed. It could also be that the referred object does not exist in the abstract machine. The operation relServRel is used to release service relations. This operation should be used as soon as an abstract machine knows that the relation will no longer be needed, thereby giving other abstract machines access to the other object. Note that the operation relServRel will not terminate the underlying con- nectivity relation, even if all service relations become released. Release of con- nectivity relations is handle by the association handler of the logical node in which the event handler resides, see Sect. 5.3.4. Figure 7.66 shows the scenario for setting up and using service relations in abstract protocols. 1. A seizeServRelReq is detected. Object references are either OBid, PSid or both. 2. OPH can distinguish between operations that are handled by the OBH and oper- ations that are defined by other service objects. OPH sends the list of OBid and PsId to OBH. 7.7 Concepts and Notations in Abstract Networks local refe- rences seizeServRelCnf seizeServRelReq SRid-opReq(...) Fig. 7.66 The scenario for service relation handling 3. OBH analyses the list and returns local object referen