Important research efforts are being conducted in the area of search, lookup, and routing, and are even increasing in the quest for P2P middleware that is both scalable and decentralized. To structure and classify current as well as facilitate and give direction to future research, this methodology proposes a top-down two-dimensional design space. This design space has been developed for exhaustiveness so as to cover all possible design options, existing or yet to be conceived. A comprehensive survey of P2P search systems serves as a reference for the reader while at the same time validating the framework. An identification of areas in the design space not covered by current systems leads to the design of a novel peer-to-peer-based keyword routing scheme. Finally, an evaluation of possible design options along the most important requirement will help guide system designers.