Information retrieval systems aim to help users find relevant information quickly and efficiently. A typical session with such a system starts with a user posing a query, in response to which the system presents a ranking of documents retrieved from a large collection, such as the web or a company document store. The user interacts with these results by examining and possible selecting (clicking on) some. The user can also follow up by reformulating the query to continue searching or can abandon the search. When finished, the user may or may not be satisfied.