Wells, Walter
Kent Publishing Company, 1985
Buku Teks
Calder, Alan, author
kogan page limited, 2005
Buku Teks
Barnes, A. James, author
Learning Systems, 1981
Buku Teks
Merriam-Webster, Inc., 1988
Buku Teks
Andrews, Dorine C., author
Yourdon Press, 1994
Buku Teks