sentences:  However, it was Terry Halpin's 1989 PhD thesis that created the formal foundation on which Object-Role Modeling is based.Bill Kent, in his 1978 book "Data and Reality," compared a data model to a map of a territory, emphasizing that in the real world, "highways are not painted red, rivers don't have county lines running down the middle, and you can't see contour lines on a mountain".In contrast to other researchers who tried to create models that were mathematically clean and elegant, Kent emphasized the essential messiness of the real world, and the task of the data modeller to create order out of chaos without excessively distorting the truth.