Design Time 
At design time, an integration developer designs the integration-relevant aspects of a business process at an abstract level, independent from any implementation-relevant details.
The following aspects of a business process can already be specified at design time:
The process flow and its separation into individual process components (or application components)
The Enterprise Services Repository (ES Repository) allows you to outline the integration-relevant aspects of business processes, for example, using a process integration scenario model type.
The interfaces that determine the data exchange between application components and the detailed structure of the data – of the messages – that is being exchanged
The mapping or transformation of data structures on both sides of a connection
In a mediated communication step, the sender normally uses a data format and structure for sending out a message that is different to the one that the receiver can handle. The data structure and format used by the sender therefore has to be transformed into the structure and format that the receiver can handle. This type of transformation is called mapping. You specify the corresponding transformation rules in the ES Repository – in the form of mapping objects.
Note
The design time-relevant aspects are specified and stored in the ES Repository. The corresponding content is referred to as integration content.
Recommendation
It is recommended to design integration content using the top-down design approach.
More information: Top-Down Design