Another challenge is the implementation of filters to select molecules according to pre-defined rules such as Lipinski's Rule of Five (ROF). Maggiora discussed the importance of 'soft' methods for selecting compounds according to ROF. Zadeh et al. define soft methods as an emerging computational approach that parallels the remarkable ability of the human mind to reason and learn in an environment of uncertainty and imprecision. Such methods tend to produce more realistic molecular property relationships as discussed by Maggiora and co-workers .