12. A method for generating query expansion rules comprising: with a computer comprising memory and a computer processor: automatically extracting candidate synonymy pairs from expressions used by users in queries when searching a knowledge base, the user queries being grouped into user sessions based on session information, each user session including a first user query input by a user and a subsequent reformulated user query input by the same user, wherein the extracting includes generating each candidate synonymy pair from a term of a first user query input by a user and a term of a reformulated user query input by the same user in the same user session; providing for interactive definition of synonymy rules based on the extracted candidate synonymy pairs and for contextualizing the synonymy rules; and exporting query expansion rules based on the defined synonymy rules to a storage medium for use in expansion of user queries when searching the knowledge base.
12. A method for generating query expansion rules comprising: with a computer comprising memory and a computer processor: automatically extracting candidate synonymy pairs from expressions used by users in queries when searching a knowledge base, the user queries being grouped into user sessions based on session information, each user session including a first user query input by a user and a subsequent reformulated user query input by the same user, wherein the extracting includes generating each candidate synonymy pair from a term of a first user query input by a user and a term of a reformulated user query input by the same user in the same user session; providing for interactive definition of synonymy rules based on the extracted candidate synonymy pairs and for contextualizing the synonymy rules; and exporting query expansion rules based on the defined synonymy rules to a storage medium for use in expansion of user queries when searching the knowledge base. 14. The method of claim 12 , further comprising filtering out synonymy pairs where the second term is absent from the knowledge base.