" Recent developments in peer to peer networks * have centered around the concept of distributed hashtables (DHT) or content routing [Ratnasamy et al., 2001][Stoica et al., 2001]. These approaches assume possession of a hash or other identifier that precisely specifies the document the user wishes to retrieve. Naturally there are some situations in which a user only has more general information about their needs, e.g. keywords or other meta-data. A number of different strategies for handling this kind of search in peer to peer networks have recently come to light. Several are summarized below along with an attempt to identify some common themes."
Description of Anthill:
" The crucial difference in their scheme (apart from calling messages ants) is that each nest (node) stores a routing table associating keyword hashes with sets of other nests. Different nests become associated with different parts of the hashed keyword space thus avoiding the problem that keyword space itself is highly clustered (presumably around various spellings of "Britney Spears")."
Covers Edutella, FASD, Anthill, Routing Indices, Alpine, Associative P2P Networks, PlanetP, Query Routing, SIONet, JXTASearch, NeuroGrid, Reptile, Semplesh, and HyperCuP.
I'll have to check these out at a later date especially NeuroGrid, SIONet, Platet and HyperCuP.