A PartSubstitutionSpecification defines a set of PartVersions that can be used alternatively, due to an incomplete specification for the 150% product description. For a concrete wiring harness only one valid PartVersion remains. The selection logic for valid PartVersions is not included in the VEC. It is NOT valid to use a PartSubstitutionSpecification for PartVersions with identical properties that just have different PartNumbers in different contexts (e.g. multi supplier topics). For these cases an ItemEquivalence shall be used.
A PartSubstitutionSpecification can be used e.g. for tubes or ring terminals, where a part of the specification is known at design time, but not yet the complete specification. E.g. for tubes the required inside diameter is not known at design time, since it depends on the bundle diameter of a specific configuration.
In order to represent a component instance that utilizes such a PartSubstitutionSpecification a PartUsage is necessary. The PartUsage is the element in the VEC which defines instances of components, where a specific PartVersion is not yet known. It references one or more PartOrUsageRelatedSpecifications to describe the known properties of the component. If the PartUsage references an additional PartSubstitutionSpecification the set of valid PartVersions can be further constrained.