An invention is described herein that provides methods and apparatus for collecting, distributing and storing product data. A data structure suitable for use in collecting, distributing or storing product data for use in a catalog is disclosed. More particularly, the data structure is based on a data model having one or more classes, where each of the classes has one or more associated categories. The data structure includes at least one class definition, each class definition being arranged to identify one or more associated categories. In addition, the data structure includes a plurality of category definitions, each category definition being arranged to identify an associated attribute group.