1. A computer-implemented method for storing data in a computer data repository, the data identifying a particular item in an electronic catalog that is described by a set of attributes including at least one attribute that has at least two alternative values used to describe the same particular item, comprising the steps of: storing in a first table data identifying at least a first item and at least first and second sub-items associated with said first item, said first item being an item in an electronic catalog and said first and second sub-items corresponding to alternative information for the same attributes of said first item; storing in a single attribute identification column of a second table at least a first and a second attribute identification associated with said first item, said first attribute identification identifying a first property of both said first and second sub-items and being repeated for each of said first and second sub-items in respective rows of the single attribute identification column, and said second attribute identification identifying a second property of both said first and second sub-items; and storing at least a first and a second attribute values for said first attribute identification in respective rows of an attribute value column within one of the second table and a third table, said first and second attribute values associated with said first and second sub-items, respectively, and being alternative values of said first property identified by said first attribute identification for said first and second sub-items respectively; wherein the first and second attribute identifications are unique identifiers and said steps of storing do not make use of a foreign key.