Abstract: Various computer implemented methods and data processing apparatus are described for use in structuring digital items and searching a plurality of digital items using a query item. At least one feature of a query digital item is extracted from a data file of the query digital item to form a query feature vector from a plurality of numerical data items representing the feature. It is determined which of a plurality of first clusters is most similar to the query digital item to identify a result cluster from the plurality of first clusters by calculating the aggregated similarity of a plurality of different digital items represented by a one of the first clusters to the query digital item for each of the plurality of first clusters using the query feature vector. Each of the plurality of first clusters represents a different plurality of digital items and each digital item is represented by only one of the plurality of first clusters.