( ( A ( pie chart ) ) ( ( is ( ( a ( circular graph ) ) ( used ( to ( ( show ( ( the relationship ) ( of ( a part ) ) ) ) ( to ( a whole ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN pie) (NN chart)) (VP (VBZ is) (NP (NP (DT a) (JJ circular) (NN graph)) (VP (VBN used) (S (VP (TO to) (VP (VB show) (NP (NP (DT the) (NN relationship)) (PP (IN of) (NP (DT a) (NN part)))) (PP (TO to) (NP (DT a) (NN whole))))))))) (. .)))
A pie chart is a circular graph used to show the relationship of a part to a whole.
(ROOT (S (NP (NNP Circle) (NNS graphs)) (VP (VBP are) (ADJP (JJ useful) (PP (IN for) (S (VP (VBG showing) (NP (NP (NNS percents)) (PP (IN of) (NP (DT a) (NN whole))))))))) (. .)))