19. The system of claim 18 , wherein the computer program product is operable to cause data processing apparatus to perform operations comprising: mining an existing symbolic knowledge resource based on a keyword; and augmenting the hierarchical knowledge structure with results of the mining to add to the knowledge represented explicitly through domain vocabulary words and relationships among the domain vocabulary words.
20. The system of claim 19 , wherein the computer program product is operable to cause data processing apparatus to perform operations comprising retrieving information from the hierarchical knowledge structure based on a received query, the retrieving comprising combining contributions of pertinence, with respect to the received query, from the discrete knowledge types.