Spark Operating Principle


I’m deliberating the client spark .At the beginning,I want to know the spark operating principle.

System commentary or detailed description is OK.

Are there some documents or resources describe the Spark Operating Principle?

Spark’s main operating principle is XMPP standard and protocols ( In the other words Spark sends an xml package with a message to a server and then server forwards that message to another client (this can be Spark or any other xmpp compliant client). Sometimes it may be a direct peer to peer connection between clients (voice chat, file transfer). So, that’s it. Not sure if i understand right what “operating principle” is.