Search fragment-coded

Today, fragment coding is still quite important in patent databases (sec Chapter 5, Section 5.11, e.g., Dei went) where Markush structures are also stored. There, the fragments can be applied to substructure or othei types of searches where the fragments arc defined, c.g., on the basis of chemical properties. 

With the variety of chemical substance representations, i.e., fragment codes, systematic nomenclature, linear notations, and connection tables, a diversity of approaches and techniques are used for substructure searching. Whereas unique, unambiguous representations are essential for some registration processes, it is important to note that this often cannot be used to advantage in substructure searching. With connection tables, there is no assurance that the atoms cited in the substructure will be cited in the same order as the corresponding atoms in the structure. With nomenclature or notation representation systems, a substructural unit may be described by different terms or... 

As with the numeric data, the content of stmctural information in the secondary literature is fimited, and we therefore have a situation in which many specicdised systems have been developed to deal with stractural data. Files of chemical stractures, and means of accessing them, have been with us for a number of years, certainly from before computers. Traditionally, these have used notations, fragment codes, etc., as the means of recording structural information, and have allowed searches to be made for complete compounds or for all compounds containing certain specified substractures. More recently, topographical systems have been developed. In these the complete stractures are recorded in the form of "connection tables", which store full details of all the atoms and bonds in a molecule, and the precise arrangement in which they are connected. 

Traditional substructure search systems work in two stages the first stage is a preliminary filter using fragment codes the second stage applies atom-by-atom search to check the isomorphism of the subgraphs. 

Whatever the search software offered, however, the database was of utmost importance. The DARC system not only offered a means to search generic structures in the short term, it also offered a way to record all of the information about structures found in patents, through a new and flexible input system. This capability was of incredible import to Derwent we could build a database that would not only serve the users today, but in future could be of more utility as search software was further developed. As opposed to the fragmentation code, there should never be a question of time-ranging. Moreover, though we assume that Markush DARC is a system not only of today but of tomorrow, we are building a database that can be converted and adapted to other search systems that may be offered by other organisations. 

At this juncture, Markush search systems for patents are fairly mature. The fragment code and graphical systems in... 

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