1. A method for assisting a user to develop a query in a natural language, comprising: storing logs comprising information derived from prior user search sessions in which user queries were input to a search engine for retrieving responsive instances from a knowledge base; storing a collection of query suggestions, each of the query suggestions formulated to retrieve at least one responsive instance in the knowledge base; ranking the query suggestions in the collection, based at least in part on the stored logs; receiving a user's query in a natural language; and while the user's query is being entered, generating a subset of the ranked collection of query suggestions and presenting at least one of the subset to the user as a candidate for a user query, the subset being based on that portion of the user's query already entered, the presentation of query suggestions in the subset of query suggestions being based on their respective rankings in the collection.