Protetch, Max
Regan Books, 2002
Buku Teks SO
edited by Angelo M. Venardos
Sweet and Maxwell, 2010
Buku Teks SO
Bateman, Thomas S.
McGraw-Hill, 2015
Buku Teks
Leading Hotels of the World, 2000
Buku Teks SO
Bayon, Damian Carlos
John Wiley & Sons, 1979
Buku Teks SO