Approximation and similarity in concept lattices

Various approaches have been proposed to perform concept approximation using a concept lattice developed from a formal context. This paper reviews several of these approaches and examines the relationships among them. Since concept approximation is also strongly related to determining the similarity between concepts within a concept lattice, a variety of methods for measuring concept similarity are presented. Several of these methods introduce the idea of concept irreducibility and approximation within the measurement of concept similarity.