Multi-diagrams of relations between fuzzy sets: weighted limits, colimits and commutativity

Abstract: Limits and colimits of diagrams, defined by maps between sets, are universal constructions fundamental in different mathematical domains and key concepts in theoretical computer science. Its importance in semantic modeling is described by M. Makkai and R. Par\'e, where it is formally shown that every axiomatizable theory in classical infinitary logic can be specified using diagrams defined by maps between sets, and its models are structures characterized by the commutativity, limit and colimit of those diagrams. Z. Diskin taking a more practical perspective, presented an algebraic graphic-based framework for data modeling and database design. The aim of our work is to study the possibility of extending these algebraic frameworks to the specification of fuzzy structures and to the description of fuzzy patterns on data. For that purpose, in this paper we describe a conservative extension for the notions of diagram commutativity, limit and colimit, when diagrams are constructed using relations between fuzzy sets, evaluated in a multi-valued logic. These are used to formalize what we mean by "a relation $R$ is similar to a limit of diagram $D$," "a similarity relation $S$ is identical to a colimit of diagram $D$ colimit," and "a diagram $D$ is almost commutative."