Artikel Jurnal
Harig, Katherine J.
Library Professional , 1989
Buku Teks SO
edited by Juan J. Linz and Alfred Stepan
John Hopkins University Press, 1978
Buku Teks SO
Linz, Juan J.
Johns Hopkins University Press, 1978
Buku Teks SO
Landauer, Carl
J. B. Lippincott, 1964
Buku Teks SO