de la Peña Zarzuelo, I., M. J. Freire-Seoane, and B. López-Bermudez. “Mission Statements in Port Authorities: Empirical Analysis of Content in Spanish Port System”. Transactions on Maritime Science, vol. 8, no. 2, Oct. 2019, pp. 235-4, doi:10.7225/toms.v08.n02.009.