We study the scaling relations of the Manna [J. Phys. A 24, L363 (1992)] model. We found that the avalanche exponent depends crucially on whether one drives the system in the hulk or at the boundary while the cutoff scaling exponent is invariant. Scaling relations relating these exponents are derived for various modes of driving. It is shown numerically that the one dimensional Manna model and a recently introduced ricepile model have the same exponents. Finally, a class of nonconserved self-organized critical models is introduced, and a classification scheme for sandpile models is proposed.
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