We describe an abstract architecture of adaptive applications, and indicate where we believe crucial design decisions must be made.We illustrate the use of the abstract model in the design and implementation ofan image proxy, and describe the studies required in determining the appropriate design points.In particular, even though adaptation to resource constraints is generally considered a systems probleu the adaptation is visible to the user in changes in utility, and so the user must be involved in designing the application.Finally, we discuss the politics that creep in when dwigners change the semantics of applications. Adapting to Constraints: Choices in Application Design An adaptive application is one in which the application changes its behaviour according to the perceived constraints in Ille envitnnnlent, so fl,rto nlaintain the semantics of the application for the lise~If we take the above definition as our starting point, then we 133 -----..-. . ... . . . .