Technically, the business logic of different process components in an integration scenario is implemented on different systems. Let us assume that the systems involved in an integration scenario communicate directly with each other. For example, if the process components run on different SAP systems, one SAP system calls another using a remote function call. We call this kind of communication “point-to-point” or direct communication. However an upgrade to one part of the system landscape would, for example, entail that all individual connections that are affected also have to be adapted as part of the upgrade. In the case of large system landscapes, this approach could easily get out of control since the number of connections grows to the square of the number of systems. However, consider a situation where a central instance interconnects the systems as a communication hub or data hub. We call this type of communication mediated communication and refer to the data hub as the integration broker. With a central instance interconnecting the systems you then have the option to have all integration-relevant information accessible at one central location. In contrast to the point-to-point scenario where there is a “spaghetti-like” arrangement of connections, in a mediated scenario the number and arrangement of connections remains manageable. The following figure illustrates the difference between mediated and point-to-point communication:
Figure 2: Point-to-point communication (left) compared to mediated communication (right)
Mediated communication based on an integration broker is executed by exchanging XML messages. Accordingly, in the context of SAP NetWeaver PI we usually speak of message-based integration. The messages contain the business data exchanged between the systems involved in a cross-component process. The message protocol of SAP NetWeaver PI (which the integration broker can process) is based on the W3C standard SOAP Messages with Attachments (see also Messages). Note: While we do cover direct or point-to-point communication (see Setting Up Direct Communication between WSRM- Enabled Systems), the main focus of this handbook is on mediated communication.