Sudoku Graph Theory

How is Sudoku related to Graph Theory?
I’ve read in an article that the solution of this game is linked to graph theory, could someone explain this to me?
Take a look at http://www.ddj.com/windows/184406436 and http://www.ddj.com/blog/portal/archives/2007/06/color_me_puzzle.html
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Categories: blog algorithms, graph, math, programming, sudoku, sudoku and graph theory, sudoku graph theory
