How the Biological Activity Spectrum is estimated by PASS?

The approach used in PASS is based on the suggestion that Activity=f(Structure). Thus, by "comparing" the structure of a new compound with structures of well-known biologically active substance it is possible to estimate if a new compound may have a particular effect. Actually, the mental work of medicinal chemists is based on this principle. However, PASS operates with many thousands of substances from the training set, so provides more objective estimate if a compound is active or not for any kind of activity as compared with any researcher.

The process of PASS development and use is shown in figure below. . .