1. A method of operating a computing system to produce clusters of items from a data set for which a subset of items from the data set has been identified, the method comprising acts of: with at least one processor, adding items to the subset, the adding comprising iteratively, until the subset has a size above a threshold size: for a candidate item, determining one or more degrees of relatedness, the one or more degrees of relatedness being a degree of relatedness to items in the subset and/or a degree of relatedness to items outside the subset; selectively adding the candidate item based on the one or more degrees of relatedness and one or more degree of relatedness criteria; and after selectively adding the candidate item, selectively removing items from the subset that do not meet at least one of the one or more degree of relatedness criteria.