DIN V 4002-7 specifies rules for the creation of a reference hierarchy and associated definion classes. The reference hierarchy suits solely the definion of properties regarding their scope of application. Product classification (in terms of product group keys) is not the purpose of the reference hierarchy and associated classes. That means that the refence hierarchy shall not be understood as a rival hierarchy for product classifications but a mean to define properties unambiguously within their scope. Thus defined and standardized properties can be used for the building of corresponding company- or branch-specific product classification in that way that the exchange of product data requires no information about the particular concrete classification. According to this the rules for the creation of user-oriented hierarchies given in this standard are recommended insistently.