Information Retrieval System

A method of retrieving a ranked list of documents from an index of documents comprising

• receiving at least one query term;
• generating a plurality of lists of documents from the index using the query term;
• predicting, for each of the lists of documents, implicit relevance information and explicit relevance information;
• calculating a utility score for each of the lists of documents using the predicted relevance information and a stored utility function;
• selecting and storing one of the lists of documents on the basis of the utility scores.

One or more device-readable media with device executable instructions for performing steps comprising:

• receiving at least one query term being part of a request to retrieve a ranked list of documents from a document index;
• generating a plurality of ranked lists of documents from the index using the query term;
• using a machine learning system comprising a stored probabilistic model to predict, for each of the ranked lists of documents, implicit relevance information and explicit relevance information;
• calculating a utility score for each of the ranked lists of documents using both the predicted implicit relevance information and the predicted explicit relevance information as well as a stored utility function;
• selecting and storing one of the ranked lists of documents on the basis of the utility scores.