Mapping

hello....

I have small question..as i am new to xi..

In mapping..

Suppose we are sending message from SAP-XI-Legacy..

I hope we need to create 2 interfaces like inbound and out bound..

in inboud interface i.e from sap to xi...source message is idoc which is imported to IR..

but what is the target message type....is this can be

message which we need to send to legacy system?

then what will we take in out bound interface?

Can any one explain me the scenario?

Thanks..