CROSSBOW connection table

The WLN was applied to indexing the Chemical Structure Index (CSI) at the Institute for Scientific Information (ISI) [13] and the Ituiex Chemicus Registry System (ICRS) as well as the Crossbow System of Imperial Chemical Industries (ICl). With the introduction of connection tables in the Chemical Abstracts Service (CAS) in 1965 and the advent of molecular editors in the 1970s, which directly produced connection tables, the WLN lost its importance. 

A search facility was provided using the CROSSBOW Bit and String search program, which is sufficient for small files but clumsy to use. However our primary aim was to obtain clean and useful WLN files, ready for conversion to a graphics system in due course, so the extra expense of connection table based searching seemed unjustified. 

We needed some way to indicate the reaction site and have devised a system based on the CROSSBOW connection table, which allows us to give a unique number for each node in the structure. For example, the above example gives us the following numbering ... 

ICRS particularly alerts novel reactions and syntheses, and the relevant abstracts can be found by searching the tapes or by scanning Index Chemicus. The first stage of the process is to isolate all the WLNs given for the relevant abstract and to display the structures with relevant CROSSBOW connection table information. 

The CROSSBOW chemical search system (1-5) is a multilevel one. Search of the bit screens is first carried out and this quickly and cheaply reduces the file to ten per cent (or less) of its original size. There will almost certainly be many false drops but most of these can usually be removed by string search of the WLNs and/or molecular formulae and/or reference numbers. String searching is slower and more expensive than bit search. Connection table generation and atom-by-atom search of the connection tables (the third search level) are still slower and even more expensive, but the atom-by-atom search program is a very powerful tool which is used in about 80% of all searches. The CROSSBOW connection tables for the hits from any search are finally used as input to a structure display program. 

An average bit and string search takes about five minutes (searching 190,000 compounds). The CROSSBOW connection table generation program handles 1500-2000 compounds a minute, and the atom-by-atom program searches 600 compounds a minute. Well over 90% of notations are amenable to connection table generation and over 90% of the compounds on the database can be structurally displayed directly from the connection table. 

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