6Freeman, Linton C. The Development of Social Network Analysis A Study in Sociology of Science, Vancouver, BC(Canada) : Empirical Press ,2004,p. 39.
7Wellman, Barry, Structural analysis From method and metaphor to theory and substance. In Wellman and Berkowitz(eds). Social Structure A Network Approach, Cambridge University Press, 1988, p. 47.
8Konke D. And J. H. Kuklinski, Network Analysis Beverly Hills Sage , 1982 ,p. 9.