1. A distributed system comprising one or more administration computers arranged in operation to at least: i) receive a plurality of digital resource identifiers and, for each identified digital resource, a set of one or more tags attributed to said digital resource; ii) generate a classification of said digital resources by automatically generating categories of said digital resources by calculating a measure or the similarity between said sets of one more tags attributed to said digital resources, each category including one or more of said digital resources; iii) generate, for display to a human user, a graphical user interface enabling modification of said classification; iv) modify said classification in accordance with user commands received via said graphical user interface; and v) utilise said modified classification in identifying one or more digital resources in said digital system; and vi) use said digital resource in said distributed system.