Semantic similarity, variously also called 'semantic closeness/proximity/nearness', is a concept whereby a set of documents or terms within term lists are assigned a metric based on the likeness of their meaning / semantic content. In mathematics, a metric space is a set (or space) where a distance between points is defined. ... Meaning, studied in philosophy and linguistics, as well as being central to the fields of literary theory and critical theory, the philosophical field of epistemology, and some branches of psychoanalysis, is a difficult concept to pin down. ... In general, semantics (from the Greek semantikos, or significant meaning, derived from sema, sign) is the study of meaning, in some sense of that term. ...

An intuitive way of displaying terms according to their semantic similarity is by grouping together closer related terms and spacing more distantly related ones wider apart. This is common - if sometime subconcious - practice for mind maps and concept maps. A mind map or mindmap is a multicoloured and image centered radial diagram that represents semantic or other connections between portions of learned material. ...

Concretely, this can be achieved for instance by defining a topological similarity, by using ontologies to define a distance between word (a naive metric for terms arranged as nodes in a directed acyclic graph like a hierarchy would be the minimal distance (in separating edges) between the two term nodes), or using statistical means to correlate words and textual contexts. Several equivalence relations in mathematics are called similarity. ... This article is about the philosophical meaning of ontology. ... A simple directed acyclic graph In mathematics, a directed acyclic graph, also called a dag, DAG, or acyclic directed graph, is a directed graph with no cycles; that is, for any vertex v, there is no directed path starting and ending on v. ... A hierarchy (in Greek hieros = sacred, arkho = rule) is a system of ranking and organizing things. ...