Eg. A -> B -> C
A more find grained view of this intergration might go:
|------------------A Codebase------------------||------------------B Codebase------------------||--------C Codebase---...
A UI -> A Controller -> B Service -> B Client -> B API -> B Controller -> CService -> CClient -> C API etc...
|---A/B pact------------------------?
|---A/B pact------------------------------------?