1. A knowledge based system for retrieving information by using a concept relation model which expresses knowledge by a plurality of interconnected nodes, each node represents a concept corresponding to information included in said node, said node being connected to other nodes by links, each of said links represents a relation between concepts represented by nodes connected by said link, comprising: a first memory for storing concept names corresponding to said nodes, each concept name corresponds to a concept; a second memory for storing information representing subsumption relations between different concepts corresponding to links connected between said concepts; a third memory for storing information representing definitions of different kinds of relations; a fourth memory for storing information representing relations between different concepts corresponding to links connected between said concepts; and relation deducting means for inputting a string of words from a user of said system and deducting both concept names and relations between concepts from said inputted string of words by using knowledge stored in said first to fourth memory; and retrieval means for retrieving information from at least one of said nodes based on said concept names and said relations between concepts deducted by said relation deducting means.