A data-flow graph (DFG) is a graph which represents a data dependancies between a number of operations. Any algorithm consists of a number of ordered operations. Since examples are always better than words, consider the procedure for finding the root of a quadratic equation (algorithm assumes real roots):

quad( a, b, c) t1 = a*c; t2 = 4*t1; t3 = b*b; t4 = t3 - t2; t5 = sqrt( t4); t6 = -b; t7 = t6 - t5; t8 = t7 + t5; t9 = 2*a; r1 = t7/t9; r2 = t8/t9;One could implement this algorithm line by line, but a more general realization would note the dependancies between each operation. For example t2 can not be computed before t1, but t3 could be computed before t1 or t2.