Discovery of resources is a frequent strategy in various protocols. XMPP calls it disco.

PSYC tries to avoid these approaches and pushes/multicasts information out to possibly interested recipients in advance. A logical enhancement of this is to keep distributed state.

While traditional approaches give you a search box where you have to think of something you want, then see if it's there, PSYC is more like a toy store where you see all the offerings with colorful pictures presented to you and you just use what you need. This makes sense especially for file sharing between friends.

See also Directory services.