The research presented in this paper ispart of a larger project of building a graphical interface for document retrieval which is based on a conceptual analysis of explicit and implicit structures among document data. Mathematical lattices, which are formalized according to Formal Concept Analysis, serve as an internal model. The lattice model is opposed to the more traditional vector space-based information retrieval models. Besides the document database a thesaurus is included in the system and also formalized as a lattice. The system obtains a high degree of flexibility, i.e. adaptability to different document, databases or knowledge bases and to changing users preferences, from its modular design and from a set of lattice combination options.