1. A method for estimating similarity between concepts, the method comprising: receiving a set of concepts related to a corpus of text documents; creating 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 deriving, 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, wherein a programmed processor device is configured to perform said receiving, creating and deriving.