This paper analyses one of the most well-known general purpose adaptive hypermedia systems, AHA!, and, based on this analysis, make some general observations about adaptive hypermedia systems and some improvement suggestions for the AHA! system. We suggest here a concept-based approach to the structuring of adaptive hypermedia systems, as well as an extension of the well-known rule-based overlay method for user-adaptation. This approach is another step towards flexible generic-purpose adaptive hypermedia.