We compare different formulations of the generalized uncertainty principle that have an underlying algebraic structure. We show that the formulation by Kempf, Mangano and Mann (KMM) [Phys. Rev. D 52 (1995)], quite popular for phenomenological studies, satisfies the Jacobi identities only for spin zero particles. In contrast, the formulation proposed earlier by one of us (MM) [Phys. Lett. B 319 (1993)] has an underlying algebraic structure valid for particles of all spins, and is in this sense more fundamental. The latter is also much more constrained, resulting into only two possible solutions, one expressing the existence of a minimum length, and the other expressing a form of quantum-to-classical transition. We also discuss how this more stringent algebraic formulation has an intriguing physical interpretation in terms of a discretized time at the Planck scale.
