Other Substructure-Based Methods

The Rekker approach is still used with revised Z/ systems, e.g., in the software program Z/SYBYL [8]. Over recent decades various other substructure-based approaches have been developed that are mostly implemented and available as computer programs. 

Several models have been published where the fragments are defined on a purely atomic level. This simplifies both the recognition of fragments and the calculation, as correction substructures are not applied (see Eq. (10)). N is the occurrence of the ith atom type. 

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Other common descriptors derived from substructure-based methods are discussed below. Among these, hash structural codes, structural keys, and fingerprints are mostly applied in virtual screening and substructure searching, whereas pharmacophore-based descriptors are more successful in similarity/diversity analysis and QSAR/QSPR studies. 

All new descriptors, QSAR approaches and chemometric strategies proposed since 2000 have been included in this handbook. Several new topics such as biodescriptors, characteristic polynomial-based descriptors, property filters, scoring functions, and cell-based methods have been added. Other topics, such as substructure descriptors, autocorrelation descriptors, delocalization degree indices, weighted matrices, connectivity indices, and so on, have been completely rewritten. 

The first interface of the Data Persistence Layer is the finder interface— the interface for querying the database. Two types of queries must be supported by a chemical information database one is numeric or text query, and the other is structure query. The first type is the same as any other type of database. The second type is where chemistry databases differ—search the database based on substructure, structure similarity, and structure flexmatch. As such, the finder interface has to support these two types of finder methods. The CompoundFinder interface is as follows ... 

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