ded to before the OPH can generate a new operation request. If an operation is declared synchro- nous, the concrete language interface can still use asynchronous primitives. In that case, the OPH must be able to buffer new operation requests until the previ- ous one is responded to (compare to the discussion in Sect. 4.5.2 about send and receive operations). An operation may be destructive to previous operations that are not yet responded to. A typical example is when an object requests a connection and then requests a disconnect before the previous request is responded to. If the dis- connect operation is defined as destructive, the OPH should try to inhibit or undo the effects of previous invocations. There are two timing aspects of interest: the time it takes to execute the opera- tion (ACTIVITY TIME) and when in time the operation may be executed (TIME CONSTRAINT). Note that the OPH level is not bound to whether concrete objects exist in the same physical node or are remote from each other. Neither is the abstract protocol bound to any specific concrete language for implementation of service objects. This is the essence of integration levels 0 (service network) and 1 (abstract net- work) in the integration hierarchy. 5.4.3 Format Handling The format handler (FOH) represents the first step in message communication between remote objects. The primary task of the FOH is to sequence the gev opera- tion parameters to a FOH message, and to identify ASP parameters in FOH mes- sage. Secondary tasks are to perform dialogue control and format error control of FOH messages. Examples of standardized FOHs are the OSI ROSE protocol and the CORBA GIOP. Compared to the operation specification in Fig. 5.24, the FOH must have access to data types for each information element of an ASP. In AML, data types can be added to a symbolic operation specification, which turns it into a typed operation specification, see Fig. 5.25 (this is an example of specification refinement). Data types are needed since in the final message (created