Extensions of closeness centrality?

The concept of vertex centrality has long been studied in order to help understand the structure and dynamics of complex networks. It has found wide applicability in practical as well as theoretical areas. Closeness centrality is one of the fundamental approaches to centrality, but one difficulty with using it is that it degenerates for disconnected graphs. Some alternate versions of closeness centrality have been proposed which rectify this problem. This paper points out that these are not true extensions of closeness centrality in the sense that they do not rank the vertices of connected graphs in the same way that closeness centrality does.