Applying adaptation spaces to support quality of service and survivability

Adaptation is a key technique in constructing survivable information systems. Allowing a system to continue running, albeit with reduced functionality or performance, in the face of reduced resources, attacks, or broken components is often preferable to either complete shutdown or continued normal operation in compromised mode. However, unpredictable adaptation can sometimes be worse than the problem it seeks to cope with. In this paper we introduce adaptation spaces, which precisely and predictably specify the adaptation of a software component. We then present two survivable systems that have been specified and implemented using adaptation spaces. The first example uses user preferences regarding quality in an audio application to guide the adaptation when available bandwidth decreases. The second trades off performance overhead with intrusion resistance for "stack-smashing" attacks. We formally define an adaptation space and show briefly how it enables certain kinds of reasoning about adaptive applications. We conclude with related work and future plans.