Similarity refers to the psychological degree of identity of two mental representations. It is fundamental to human cognition since it provides the basis for categorization of entities into kinds and for various other cognitive processes.[1] It underpins our ability to interact with unknown entities by predicting how they will behave based on their similarity to entities we are familiar with.[2] Research in cognitive psychology has taken a number of approaches to the concept of similarity. Each of them is related to a particular set of assumptions about knowledge representation.