An electronic catalog is provided that stores items and attributes associated with the items. One or more of the attributes may have more than one value. Items are stored in an item table with different attributes for items stored in different rows in an attribute table. Additional items may be added to a catalog by adding additional rows to the item table, with attributes related to the additional items added as rows into the attribute table. Particular attributes may have multiple values, and attributes with multiple values are associated with sub-items that correspond to different attribute trees or attribute sets associated with the item. Searching can be performed for attribute values and search results returned indicating all items and sub-items that satisfy the search criteria.