1. A method of expanding a search expression comprising: determining, by one or more processors, two or more nodes representing two or more query terms of a search expression, wherein the two or more nodes each have an associated text for search term expansion and represent at least one concept in a semantic graph of nodes that represents a domain of semantically related concepts; determining, by the one or more processors, a center of focus within the semantic graph for the two or more nodes based, at least in part, on a spreading activation in the semantic graph; determining, by the one or more processors, a contextual relevance for the two or more nodes with respect to node the center of focus; selecting, by the one or more processors, for a query term, which is included in the two or more query terms of the search expression, at least one node from the two or more nodes based, at least in part, on a contextual relevance between the at least one node and the query term; and expanding, by the one or more processors, the search expression using an associated text of the at least one node.