In CSDL 6.1 change: An entity type can inherit from another entity type by specifying it as its base type. An entity type inherits the key as well as structural and navigation properties of its base type. To:  An entity type can inherit from another complex type or entity type by specifying it as its base type. If the base type is a complex type, the derived entity type must define a key that consists of one or more references to structural properties..  If the base type is an entity type, the derived entity type inherits the key as well as structural and navigation properties of its base type.