In the exchange of information in a peer-to-peer information system network, the problem of semantic interoperability of the communication system used by the agent associated with every peer is addressed not by imposing a universal pre-defined ontology over universally defined conceptual schemata, but instead using mechanisms, inspired from natural language, that enable each agent to develop a repertoire of grounded categories and labels for these categories and to negotiate their use and semantics with other agents. The communication system, as well as its semantics, is hence emergent and adaptive instead of predefined.