Donnelly, Daniel
Page One Publishing, 2011
Buku Referensi
Crowe, Mary
MacIntyre Purcell Pub, 2010
Buku Teks SO
Adi Kusrianto
Elex Media Komputindo, 2009
Buku Teks SO
Laurel Saville, Steve Gordhan, Jodhua Berger, Sarch Dougher, editor
Page one publishing pte ltd, 2011
Buku Referensi
Jain, Poonam
Sterling Publishers Pvt. Ltd, 2003
Buku Teks SO