Sampling a random derivation from the chart consists of choosing at random one of the fragments from the set of composable fragments at every labeled chart-entry (in a top-down, leftmost order so as to maintain the LFG-DOP derivation order).
the competition set of composable fragments is computed on the fly at each derivation step during the Monte Carlo sampling process by grouping the f-structure units that unify and that are coherent with the subderivation built so far.