[Mary] took her grandson, [William], to the zoo. [William]'s sister, [Alberta], had to stay home because she was sick.
('Mary', 'Alberta')
[Mary] took her grandson, [William], to the zoo. [William]'s sister, [Alberta], had to stay home because she was sick.
[{('Mary', 'granddaughter', 'Alberta'): [('Mary', 'grandson', 'William'), ('William', 'sister', 'Alberta')]}]