In addition to this main fragment library, the pre-existing Open Babel database of generic ring fragments was retained. This includes ∼1,000 of the most common ring fragments from analysis of the NCI Open Database and ZINC , as well as ring templates from 3 -18 atoms in size, stored as generic SMARTS patterns . This additional library is intended to ensure other ring fragments not explicitly covered in the larger fragment database have approximate matches (e.g., if the stereochemistry or elemental composition differs slightly). Using this auxiliary database is discussed below.