In this paper we describe techniques for the discovery and construction of user profiles. Leveraging from the emergent data web, our system addresses the problem of sparseness of user profile information currently faced by both asserted and inferred profile systems. A profile mediator, that dynamically builds the most suitable user profile for a particular service or interaction in real-time, is employed in our prototype implementation. Categories and Subject Descriptors: H.3.4, H.3.5 [Information Storage and Retrieval]: Systems and Software ? User profiles and alert services; Online Information Services ? Data Sharing. General Terms: Design, Management.