  In this paper we study the notion of knowledge from the positions of
universal algebra and algebraic logic. We consider first order knowledge which
is based on first order logic. We define categories of knowledge and knowledge
bases. These notions are defined for the fixed subject of knowledge. The key
notion of informational equivalence of two knowledge bases is introduced. We
use the idea of equivalence of categories in this definition. We prove that for
finite models there is a clear way to determine whether the knowledge bases are
informationally equivalent
