Wraf uses interfaces to other sources in order to integrate all data in one enviroment, regardless of storage format. You can read and update information from configuration files, databases, XML files, LDAP, etc.
The service collects information from diffrent sources through interfaces. The answer to requests depend on which interfaces the session has connected to.
Each combination of connected interfaces is given a unique key called IDS. Every IDS has it's own cache. The idea is that it in the common case will be many sessions using the same IDS cache.
It's one thing to be the owner or home interface of a node, and antoher thing to say something about the node or with the node. If we want to know everything said about a thing, we will have to search all interfaces that could give a part of the answer. But if we only want to know whats said from a limited number or sources, we can restrict the search to the interfaces that handles the models owned by the source we are intrested in.