To execute the prediction, PASS requires a knowledge base about structure-activity relationships for compounds with known biological activities. This is provided by SAR Base, containing the analysis results obtained with an in-house training set of more than 250,000 compounds with known biological activities. This training set is continuously curated and expanded. SAR Base can also be replaced by an exclusive knowledge base, which can be created using in-house data. The knowledge base together with the user-defined constraints of biological activities of interest and relevant parameters provides PASS the starting point for the computational prediction.