Soundex was originally developed by Margaret K. Odell and Robert C. Russel at the U.S. Bureau of Archives to simplify census taking in the early 1900s. Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. The goal is for data elements to be encoded to the same representation so that they can be matched despite minor differences in spelling. Surnames that sound the same but are spelled differently have the same code and are filed together. This system was developed to make it easier to find a particular name even though it may have been spelled (or misspelled). Soundex is the most widely known of all phonetic algorithms, as it is a standard feature of MS SQL and Oracle.
Over time, additional variations to Soundex have been created. A similar algorithm called “Reverse Soundex” prefixes the last letter of the name instead of the first. In 1970, the NYSIIS algorithm was introduced by the New York State Identification and Intelligence System as an improvement to the Soundex algorithm. NYSIIS handles some multi-character n-grams and maintains relative vowel positioning, whereas Soundex does not. As a response to deficiencies in the Soundex algorithm, Lawrence Philips developed the Metaphone algorithm in 1990 for the same purpose as Soundex. Philips developed an improvement to Metaphone in 2000, which he called Double Metaphone. Double Metaphone includes a much larger encoding rule set than its predecessor, handles a subset of non-Latin characters, and returns a primary and a secondary encoding to account for different pronunciations of a single word in English.