How the descriptors are computed is another fundamental aspect. Many descriptors are conformationdependent: descriptors computed only for a single conformer may not adequately represent more flexible ligands. Should a Boltzmann population average be used instead, a conformational search (hence time) must be added to the computation. A significant advantage of some available databases (e.g., Kraken and Oscar described above) is their computed descriptors, which may be used by other model developers.