  Consider a scenario where $N$ separated quantum systems are measured, each
with one among two possible dichotomic observables. Assume that the $N$ events
corresponding to the choice and performance of the measurement in each site are
space-like separated. In the present paper, the correlations among the
measurement outcomes that arise in this scenario are analyzed. It is shown that
all extreme points of this convex set are attainable by measuring $N$-qubit
pure-states with projective observables. This result allows the possibility of
using known algorithms in order decide whether some correlations are achievable
within quantum mechanics or not. It is also proven that if an $N$-partite state
$\rho$ violates a given Bell inequality, then, $\rho$ can be transformed by
stochastic local operations into an $N$-qubit state that violates the same Bell
inequality by an equal or larger amount.
