Evolving the system's core: a case study on the identification and characterization of key developers in Apache Ant - Oliva, Gustavo Ansaldi; Silva, José Teodoro da; Gerosa, Marco Aurélio; Santana, Francisco Werther Silva; Werner, Claudia Maria Lima; Souza, Cleidson Ronald Botelho de; Oliveira, Kleverton Carlos Macedo de (Computing and Informatics, 2015)