The new field of knowledge federation and the existing field of knowledge organization share quite a number of objects of experience and understanding. In particular, they have the common objective of facilitating insight by supporting gradual subject-centric organization of knowledge (of inter-related concepts and of information resources relevant to such concepts) in an environment which is conceptually heterogeneous and where the federation of scattered knowledge fragments is impeded by obstacles on several layers. The Topic Maps approach is particularly apt for tackling such obstacles, both on the conceptual and technical level, i.e. likewise for humans and the Semantic Web.

This paper reviews and discusses crucial issues of joint interest for these field from a modern knowledge organization perspective. It contributes to the advancement of knowledge federation research by reinterpreting basic ideas of conceptual knowledge organization in the light of new knowledge federation challenges pertaining to discourse communities with open, emergent knowledge systems.

The paper highlights how modern (distributed) knowledge organization (and distributed knowledge management) approaches, combined with Topic Maps, may cross-fertilize with and facilitate knowledge federation. Determining the relevance of an information resource to a concept, and thus determining its subject, is a hermeneutic act somehow relative to the interpreter. Different communities and usage contexts entail validly differing viewpoints, leading to differing conceptualizations. However, traditional knowledge organization and traditional knowledge management ultimately had to force different viewpoints into one, centralized homogeneous conceptual system (e.g. a taxonomy). The internet increased conceptual heterogeneity and brought us a more democratic, user-contributed subject organization, lately e.g. in the form of folksonomies and tagsonomies (cf. the tagsocratic project).