A Product_occurrence is a Product_specification_or_set that has position in an assembly or role in an activity as a criterion for membership.
EXAMPLE - The driven end bearing of the J. Bloggs and Co. pump type XYZ_1234 is a Product_occurrence. The impeller end bearing of the J. Bloggs and Co. pump type XYZ_1234 is a different product_type_occurrence.
These two bearings can be occurrences of the same Specific_product_specification.
EXPRESS specification:
*) ENTITY Product_occurrence SUBTYPE OF (Product_specification_or_set); END_ENTITY; (*