Yerbury, Hilary
University of Technology, 1992
Buku Referensi
Osborne, Larry N.
Libraries Unlimited , 2000
Buku Teks SO
Brown, Adrian
Facet Publishing, 2006
Buku Teks
by Nancy McCormark and Catherine Cotter
Chando, 2013
eBooks
Batley, Sue,a uthor
Chandos Publishing, 2007
Buku Teks SO