(S (S (ADVP (RB However)) (COMMA ,) (S (NP (BASENP (DT the) (NNP Mach) (NN kernel)) (VP (VP (VP (ADVP (RB first)) (VBN developed)) (ADVP (BASENP (NN ten) (NNS years)) (RBR earlier))) (PP (IN at) (BASENP (NNP Carnegie) (NNP Mellon) (NNP University))))) (VP (VBZ is) (VP (VP (VBN seen) (PP (IN as) (BASENP (DT a) (JJ flawed) (JJ first) (NN implementation)))) (COMMA ,) (PP (IN with) (S (NP (BASENP (DT the) (NNS lessons)) (VP (VBN learned))) (VP (VBG being) (VP (VBN implemented) (PP (IN in) (NP (NP (BASENP (NNS microkernels)) (PP (IN like) (BASENP (NNP L4)))) (COMMA ,) (VP (VBN known) (PP (IN as) (BASENP (JJ second-generation) (NNS microkernels)))))))))))))) (PERIOD .))