Trees Hierarchical-. HTSS

The Hierarchical Tree Substructure Search (HTSS) system [25-27] generates a single rooted decision tree from database structures by gradually refining classification of... 

A rather different approach to substructure searching is used by at least two systems. One of these is the Chemical Information System (CIS) developed by Richard Feldmann and his colleagues at the National Cancer Institute, and its various off-shoots which include the Chemical Databank System (CDS) at the SERC Laboratory in Daresbury. The other is the Hierarchic Tree Substructure Search (HTSS) developed in Hungary. ... 

HTSS is also rather similar, except that in building the hierarchic tree structure, once all the immediate neighbours for the central atom have been processed, what amounts to a relaxation procedure is applied to extend the tree search file, taking... 

CAS = Chemical Abstracts Service CT = connection table HTSS = hierarchical tree substructure search lO = input-output RDBMS = relational database management system SEMA = stereochemically extended Morgan algorithm. 

HTSS. The HTSS system developed by Nagy utilizes a hierarchical classification of all the atoms in a database collection. This is a decision tree which takes into account local atomic properties (bond orders, ring membership, etc ), then classifies atoms with respect to their first-order atomic environment, second order, and so on (Figure 5). This process has many similarities to the relaxation-ba.sed approaches to screening discussed previously, but generate.s this information at registration time for each atom in the database. 

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