The UML term pair that captures complementary ways of looking at a relationship is "aggregation / composition". Both terms describe types of associations between classes but differ in the degree of ownership and lifecycle dependency between the involved objects. Aggregation implies a weaker relationship where the parent class contains or is linked to other classes but does not strictly control their lifecycle (e.g., a university and its students). Composition, on the other hand, implies a stronger relationship where the parent class has full responsibility for the lifecycle of the associated classes (e.g., a house and its rooms). Understanding these relationships helps model systems more accurately in terms of object ownership and lifecycle management.