Reflective Designs — An Overview

AbstractWe render runtime system adaptations by design-level concepts such that running systems can be adapted and examined at a higher level of abstraction. The overall idea is to express design decisions as applications of design operators to be carried out at runtime. Design operators can implement design patterns for use at runtime. Applications of design operators are made explicit as design elements in the running system such that they can be traced, reconfigured, and made undone.Our approach enables Reflective Designs: on one side, design operators employ reflection to perform runtime adaptations; on the other side, design elements provide an additional reflection protocol to examine and configure performed adaptations. Our approach helps understanding the development and the maintenance of the class of software systems that cannot tolerate downtime or frequent shutdown-revise-startup cycles.We have accumulated a class library for programming with Reflective Designs in Squeak/Smalltalk. This library employs reflection and dynamic aspect-oriented programming. We have also implemented tool support for navigating in a system that is adapted continuously at runtime.Note: This extended abstract summarises our full paper [Hirschfeld, R. and R. Lämmel, Reflective Designs, IEE Proceedings Software (2004), Special Issue on Reusable Software Libraries. To appear. Available at http://homepages.cwi.nl/~ralf/rd/]