( ( Definition ( Atomic masses ) ) ( ( are ( defined ( in ( terms ( of ( a ( reference mass ) ) ) ) ) ) ) ; ) )
(ROOT (S (NP (JJ Definition) (JJ Atomic) (NNS masses)) (VP (VBP are) (VP (VBN defined) (PP (IN in) (NP (NP (NNS terms)) (PP (IN of) (NP (DT a) (NN reference) (NN mass))))))) (: ;)))
Definition Atomic masses are defined in terms of a reference mass;
(ROOT (S (NP (NP (DT The) (NN sum)) (PP (IN of) (NP (NP (DT the) (NNS masses)) (PP (IN of) (NP (NP (DT the) (NNS atoms)) (PP (IN in) (NP (DT the) (NN formula)))))))) (VP (VBZ is) (VP (VBN referred) (PP (TO to) (NP (RB as) (JJ molecular) (NN mass))))) (. .)))