1. A method comprising the steps of: a computing entity: storing a training data set comprising previously executed operation pairs, attribute data, and relative cost data, the attribute data for each previously executed operation pair comprising first attribute data for a first previously executed operation and second attribute data for a second previously executed operation, the relative cost data for each previously executed operation pair comprising a relative cost indicator between the first and second previously executed operations, wherein the relative cost indicator is a value representing a comparison between respective costs of the first and second previously executed operations; forming a predictor from the training data set; and applying the predictor to an operation pair of first and second to-be-executed operations to determine a predicted relative cost between the first and second to-be-executed operations.