Half is part of Whole. Half is related to Percentage. Percentage is related to Sale. 
Barrel is related to Gun. Gun is related to Piece. Piece is related to Column. 
Whole <--PartOf-- Half <--RelatedTo--> Percentage <--RelatedTo--> Sale 
Barrel <--RelatedTo--> Gun <--RelatedTo--> Piece <--RelatedTo--> Column 