Stallings, William, author
Macmillan, 1988
Buku Teks
Buchanan, Bill, author
Kluwer Academic Publishers, 1999
Buku Referensi
Sippl, Charles J., author
Macmillan, 1985
Buku Referensi
Markley, Richard W.
Prentice-Hall, 1990
Buku Teks
Skees, William D.
Lifetime learning , 1981
Buku Teks