REQIF13 — Lack of Clarity for SpecRelation source and target

In the SpecRelation section, the definition of the source and target fields for Associations is vague. There is no clear guidance in the standard for how the source/target fields map to the supplier/client relationship defined in UML. This can lead to inconsistencies in handling between tools. Consider a scenario in which you have a software requirement that derives from a product requirement. In UML, the product requirement is the supplier and the software requirement is the client (relationship would be an arrow from the software requirement to the product requirement with a dervieRqt specification). How should the export look for the SpecRelation in regards to the source and target fields?