What does "compex" refer to in "complex queries" on unstructured overlays for P2P architecture?

About P2P, I know that structured overlays are good for exact-match query. And I read that unstructured overlays are good at complex query. I didn't understand what "comp开发者_如何学运维lex" refer to here, in what sense or logic ?

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Make sure you understand what "structured overlays" means. Structured p2p networks are actually distributed hash tables that work with KEY/VALUE pairs (like a simple hash table).

Ill try to make it much simpler, Lets say you are connected to a p2p network and you'd like to download a new song. First you have to find resources, how do you do that?

In structured p2p networks (DHT) you have to take the filename and creates a key by passing it through an hash/checksum function - Now you got the key, the next step is finding the peer that stores this key => the network is organized, the routing process is based on the key.

Do you see the problem here?

These keys are uniqe, It means you need the EXACT key in order to reach the peer which stores the needed information. For example, It makes keywords search operation quite difficult.

"New_song.mp3" and "new_song.mp3" will produce completely different keys.

Then if someone in the network shares the file - "New_song.mp3", you wont find it by searching "new_song.mp3".

In unstructured a peer just flood the network with a search query - It is not a key based routing which makes it alot easier to handle such search queries.

To solve this "problem", we can publish many keys of the filename's variations.

(lower case, upper case, without spaces / extension, etc)

Thats how Kademlia network solves this problem.