Next, the teams working on adjacent layers meet, and together they flesh out the interfaces that their layers share. If you know that the client application needs to log in, then you know that a log in call must exist in the web server layer. The teams collaborate and come to an agreement on the method names and signatures. You then code each method but return only canned data. For example, a dummy login routine always succeeds if your name is Fred and fails for any other user.