Please let me know in which layer Integration specific rules should be present.As in PEGA we have Framework layer,Implementation layer,Divisional layer and Organisational Reuse Layer. So If a normal application has some 3 or 4 web services which layer they should be present.
This very much depends on how reusable your integration rules are. Usually, integration rules are very specific to an implementation so consider placing them at the implementation layer first. If the need arises, "promote" them accordingly so you can reuse across a higher layer.