Discovering local centers of concepts. The strengths of the relationships between concepts vary greatly. A concept island is a group of concepts that are closely related among themselves but marginally related to concepts outside the group. Give a concept islands, we can infer the importance of concepts by identifying local centers via social network analysis. If we connect any two concepts i and j that are directly related within an island via path pij, a network will be constructed. The length of p is the total number of concepts on p minus 1. If a pair of concepts is related transitively, the length of p is greater than 1. Island center c* can be found by looking for the concept(s) that has the shortest total path connecting to the rest of the concepts on the same island (the total is M), as shown in Formula (1).