Types of Structure Search

The advantage of structure searches consists of bypassing the problem of nomenclature for an exact structure and, moreover, retrieving all compounds belonging to one class of compounds at the same time. On a benzene ring, for instance, various substituents can be searched, or all salts and multicomponent substances along with the acid. 

In order to carry out separate searches for those various problems four types of structure queries have to be distinguished. 

During an Exact Structure Search (EXA) (Sect. 7.2.4) only those substances which exactly match the query are searched, additional substituents are disregarded (Fig. 99). Multicomponent substances or salts are excluded. The query s result may consist of more than one piece of information, because all stereo isomers or isotope compounds, for example, match the search profile exactly. 

Like the Exact Structure Search, Family Searches (FAM) also do not allow further substitutions. The result consists of compounds that match exactly the request, and also of multicomponent substances as well as salts, such as the potassium salt of piceol in Fig. 100. 

Closed Substructure Search (CSS) is a restricted substructure search. It can only be executed by special commands (Sect. 7.2.3.4), which allow substitution at certain positions, as shown in Fig. 101 piceol in or Ao-position. 

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The simplest type of structure search is the identity, or exact match, search. Testing a pair of explicit structures for identity is a problem that has been solved, and for which efficient algorithms now exist [4]. Even between explicit structures, identity comparison can become complicated when issues such as tautomerism, oligomerization, and idiomatic differences in representation (Fig. 5) are considered. 

Exact Match Search. One type of structure searching in which a query molecule is searched for in a database of structures. To exactly match the query, the target structure must be topologically identical and not be a substructure or superstructure of the query. 

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