The HasFieldDescriptionSetMandatory is a concrete ReferenceType and can be used directly. It is a subtype of HasFieldDescription.

The semantic of this ReferenceType is, in addition to the semantic of its supertype, to indicate that the field shall be provided, although it is defined as optional field in the Structured DataType.

This ReferenceType shall only be applied to fields declared as optional, i.e., fields having IsOptional set to true of Structured DataTypes with StructureType StructureWithOptionalFields.