Maps Com, 2007
Buku Referensi
edited by B.M. Willet
George Philip and Son, 1981
Buku Referensi
Griffith, Martin, author
Routledge, 2002
Buku Teks
edited by Beth A. Simmons and Richard H. Steinberg
Cambridge University Press, 2006
Buku Teks
Spero, Joan Edelman, author
Wadsworth, 2010
Buku Teks