This paper, founding on the discussions by S. F. Nadel, intends to explicate the role concept using digraphs. Nadel captured the role, focusing on its internal structure, as the hierarchy including 3 grades (that is, pivotal, relevant, andpe ripheral). we can formulate this internal structure of role by simple digraphs, if we translate Nadel's “attributes” as “nodes” and “implicitness” as “arcs”, furthermore if we permit the procedure of condensation by strong components. Acquired these role digraphs, innumerable non-role digraphs can be classified into three types, and finally three paterns of structural change of roles will be taken out.
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