Addition to section 1.8 Architectural Background

Add the following suggested verbiage at line #174: While loosely coupled it is important to understand some typical message exchange patterns to understand how business processes are tied together through an SOA. [SOA-RA] section 4.3.2.1 describes how message exchange patterns (MEP) are leveraged for this purpose. While [SOA-RA] describes two types of MEPs, event notification and request response it also notes that, "This is by no means a complete list of all possible MEPs used for inter- or intra-enterprise messaging". Three types of MEPs can inform the discussion on energy-interop integration; a one way MEP, which differs somewhat from an event notification MEP in that no response is required from the service provider, although the service consumer may receive appropriate http messages, e.g. 404 error. Figure 1 : One-way MEP where no response is expected from the other party Additional a two-way MEP and a callback MEP are specific types of request/request MEPs described in [SOA-RA] that are used in energy-interop. A two way MEP exchange pattern assumes that after a service is consumed an acknowledgement is sent. This acknowledgement is made up of the message header of the returning service, and may include a standardized acknowledgement payload, ie, for capturing errors, (or no errors is the service was called successfully). Figure 2 : Two-way MEP where after a service is consumed an acknowledgment is provided to the service consumer The callback MEP is similar to the request/response pattern described in [SOA-RA] except that it is more specific. In a callback MEP the service provider will send an acknowledgement upon receiving a request, however, once the service provider completes the corresponding business process, it will become a service consumer, by calling a service of the previous consumer, where it turn it will receive its own acknowledgement. Figure 3 : Callback MEP where a service provider sends an acknowledgement to the service consumer, performs a corresponding activity to act on the service request, then in turn makes a service request to the original initiating service consumer and receiving an acknowledgement in return