1. A system for estimating similarity between concepts comprising: one or more content sources providing content; a programmed processor device for coupling to said content sources and configured to: receive a set of concepts related to a corpus of text documents in a content source; create a representative graph structure having graph nodes each representing a latent semantic analysis (LSA) vector associated with a concept, and a node having one or more graph edges, each graph edge representing a strength of a relation between concepts based on an ontology; and derive, for a concept, a new or modified vector represented by a node in the graph by propagating the LSA vectors against said graph structure, said new or modified vector representing a modified estimated similarity between concepts.