Design a database for ranksum null distributions

[ozgunbabur]

Design a database to store ranksum null distributions (each distribution is a histogram represented with a dictionary) for different list sizes and target sizes.

Ideally, all those null distributions should be pre-calculated and the p-value calculations should be done by lookup operations. In practice, we may not have the perfect database, so something may be missing in it. The software needs to complete those missing distributions as they are needed.