The relationship between FEA and ISD Model

In the third class, I asked Jerry a question that what is the relationship between Front-End Analysis which confused me from the first begining of the course. Whether FEA is part of the model, and if it is, what the role it is playing in the model. Then he gave me the answer that it depends on what kind of model it is. Sometimes FEA does play part of the role in the model, while in some other models there's even no FEA at all. For example, the ADDIE model we are familiar with, FEA is the A-analysis part of the model. As for Gentry's Instructional Project Development and Managment Model, there's even no FEA envolved in, but only development components and supporting components communicate with each other. So, maybe in my ISD model, I have flexble choice whether include FEA or not depend on my way of solving the problem.