Process Components Interaction Model 
In the process components model (SAP ProComp model) you model the operations and service interfaces of a process component from the provider view: In the integration scenario model (SAP integration scenario model) you model the dependencies between the different process components of a value chain. To complete the communication the details between the different process components are missing. The process components interaction model (SAP ProComp interaction model) fills these gaps. You can only model a process components interaction model for an enterprise service interaction.
The following graphic displays the typical structure of such a model:
Typical Structure (Without Mappings)
The model shows in detail how two process components interact with each other. The service interfaces here are the same as those that you modeled in the process components model. In addition, there are also the message types required for communication:
A message type is required for an asynchronous operation without mapping.
Two message types are needed for a synchronous operation without mapping (one for the request and one for the response).
If the message type structures from the sending and receiving process components do not agree, the message types must be mapped on to each other using a mapping (not shown in the graphic above). You therefore need an outbound and a target message type, rather than just a message type.
The sequence of events for the message exchange is not dictated by fixed rules in the model. SAP recommends that you represent the sequence of events from top to bottom.
To exchange messages with a partner process component you will need to know for later implementation, which service interfaces and operations the business partner has intended for communication. Align yourself with your business partner and model these service interfaces and operations in the partner process component.
SAP uses interface patterns to model the message exchange between two process components with the help of asynchronous and synchronous operations. You can choose from the following interface patterns:
Asynchronous Interface Patterns:
Request Confirmation: Interface pattern for updating data (typical use case: purchase orders).
Notification: Interface pattern for target-oriented messages which are expected.
Information: Interface pattern for broadcasting events to multiple receivers.
Synchronous Interface Patterns:
Query Business Object in A2A Communication: Interface pattern for reading data using selection criteria.
Read Business Object in A2A Communication: Interface pattern for reading data using an ID.