The A, B, C's of the AWLN (Advanced Wiswesser Line Notation)

Currently, some 6 million chemical structures exist in the chemical literature, and the list is growing at a rate of 200,000 per year. Wiswesser Line Notation was developed in 1951 as a chemical information management system. It has been revised to Advanced Wiswesser Line Notation (AWLN) to provide standardized chemical formulae in linear notation for the standard typewriter and online computer terminal keyboard. The AWLN presents linear sequences of symbols, including numerals, letters, and punctuation marks, to define molecular structures. Capital letters are used to denote atoms or atomic groups. Numerals are used to denote the absolute value of ring sizes or chain lengths. Punctuation marks indicate connection or disconnection. Lower case letters serve to locate relative ring positions, and are used in the familiar 2-letter atomic symbols. AWLN can operate totally online.