When you create message interfaces you have to define a series of communication parameters, which are described below. These parameters determine how the message interface will be used and the mode of communication. The communication parameters for imported RFCs and IDocs are defined by their definition in the SAP system (or are defined implicitly; IDocs are always asynchronous).
These characteristics determine the direction of an interface:
· An outbound interface sends a request message that is only used to make a communication party aware of data sent, without waiting for a response message. In the case of the latter, we also refer to publishing interfaces.
· An inbound interface receives a request message that you reply to with a direct response message or whose data you can process in the system without a response.
To enable two components to communicate with each other using XI, you require an interface pair comprising an inbound and an outbound interface. For example, you can assign an outbound message interface to an inbound message interface or to an RFC interface that replaces the inbound counterpart (and the other way around). Therefore, RFCs and IDocs are also referred to as outbound or inbound interfaces, regardless of which side of communication they are used on.
The execution of cross-component integration processes in XI takes place on the Integration Server, that is, after a message has been sent and before a receiver has received it. An integration process receives and sends messages by using abstract message interfaces. Message interfaces of this category can perform the role of an inbound or outbound interface within integration processes, depending on whether it is used to send or receive a message. For this reason, no direction is specified during definition. In integration processes, you can use the same abstract interface to receive and send a message. Abstract message interfaces generally receive the message from an outbound interface of a sender system and send it to an inbound interface of a receiver system, thus performing a complementary role.
You also use abstract message interfaces for particular adapters (see also: Communication Parties (Case Examples)). You cannot generate proxies for message interfaces of this category since abstract interfaces are not designed to be implemented in an application system.
A distinction is made between synchronous and asynchronous communication for both imported interfaces and message interfaces. You define the mode of communication when you define an interface:
· In the case of synchronous communication, a response message is expected from the receiver after a request has been sent. Once the request message has been sent, no further messages can be sent until the response to the request has arrived back at the sender system.
· However, in asynchronous communication a (immediate) response is not expected. A sending process can send multiple messages to a receiver in a bundle and then continue executing the process.
The pair of interfaces must have the same mode.
The following graphic shows how the mode and direction of interfaces influence message exchange between interfaces: