Abstract: A computer system has storage for data files and can store and retrieval of files in accordance with a folder structure. The system is able to associate a file with more than one folder. Upon receipt of a request to store a file, it determines a measure of degree of association between the file and each of a plurality of folders of the structure; on the basis of these measures it selects folders to associate the file with, and stores the measure in respect of each of the selected folders.