Artikel Jurnal
Payne, Wayne A., author
McGraw-Hill, 2002
Buku Teks
Critten, Peter, author
Churchill Livingstone, 1996
Buku Referensi
Hackos, JoAnn T., author
John Wiley & Sons, 1994
Buku Referensi
Bigelow, Robert P., author
Upper Saddle River, NJ: Prentice Hall, 1975,
Buku Referensi