 The run-time system maintains this illusion by replicating data automatically as needed and maintaining consistency between the copies.His PhD thesis, under Tanenbaum's supervision, was sufficiently influential that it was later published by Prentice-Hall as a book entitled "Programming Distributed Systems".After getting his PhD degree, Bal was a postdoctoral fellow at MIT in Cambridge, Massachusetts, at the University of Arizona in Tucson, Arizona, and at Imperial College in London.