Heijden, Adrianus F.Th. van der, author
Bezige Bij, 2007
Buku Teks
Globe Asia Magazine,
Majalah, Jurnal, Buletin
Bartholomew, John Ryan, author
Tiara Wacana Yogya, 2001
Buku Teks
Chris Valentina, author
2018
UI - Tugas Akhir
Rabotin, Maureen Bridget, author
American Society for Training & Development, 2011
eBooks