The value of 'hrStorageIndex' corresponding to the directly
associated conceptual row in the 'hrStorageTable' representing:
a) the first underlying 'physical' storage (if any), if this
row has 'xcmHrStorageRealization' of 'logical...'; or
b) the first subordinate 'physical' storage (if any), if this
row has 'xcmHrStorageRealization' of 'physical...'; or
c) zero if there is no underlying or subordinate 'physical'
storage associated with this row (ie, this storage).