Soundex

Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. The goal is for homophones to be encoded to the same representation so that they can be matched despite minor differences in spelling.^[1] The algorithm mainly encodes consonants; a vowel will not be encoded unless it is the first letter. Soundex is the most widely known of all phonetic algorithms (in part because it is a standard feature of popular database software such as MySQL^[2], MS SQL Server^[3] and Oracle^[4]) and is often used (incorrectly) as a synonym for "phonetic algorithm". Improvements to Soundex are the basis for many modern phonetic algorithms.^{[citation needed]}

History

Soundex was developed by Robert C. Russell and Margaret K. Odell and patented in 1918^[5] and 1922.^[6] A variation called American Soundex was used in the 1930s for a retrospective analysis of the US censuses from 1890 through 1920. The Soundex code came to prominence in the 1960s when it was the subject of several articles in the Communications and Journal of the Association for Computing Machinery, and especially when described in Donald Knuth's The Art of Computer Programming.^[7]

The National Archives and Records Administration (NARA) maintains the current rule set for the official implementation of Soundex used by the U.S. Government.^[1] These encoding rules are available from NARA, upon request, in the form of General Information Leaflet 55, "Using the Census Soundex".

Rules

Different from the original algorithm, the algorithm in American Soundex is as below.

The Soundex code for a name consists of a letter followed by three numerical digits: the letter is the first letter of the name, and the digits encode the remaining consonants. Similar sounding consonants share the same digit so, for example, the labial consonants B, F, P, and V are each encoded as the number 1.

The correct value can be found as follows:

1. Retain the first letter of the name and drop all other occurrences of a, e, i, o, u, y, h, w.
2. Replace consonants with digits as follows (after the first letter):
   • b, f, p, v => 1
   • c, g, j, k, q, s, x, z => 2
   • d, t => 3
   • l => 4
   • m, n => 5
   • r => 6
3. Two adjacent letters (in the original name) with the same number are coded as a single number; also two letters with the same number separated by 'h' or 'w' are coded as a single number, whereas such letters separated by a vowel are coded twice. This rule also applies to the first letter.
4. Continue until you have one letter and three numbers. If you run out of letters, fill in 0s until there are three numbers.

Using this algorithm, both "Robert" and "Rupert" return the same string "R163" while "Rubin" yields "R150". "Ashcraft" and "Ashcroft" both yield "A261" and not "A226" (the chars 's' and 'c' in the name would receive a single number of 2 and not 22 since an 'h' lies inbetween them). "Tymczak" yields "T522" not "T520" (the chars 'z' and 'k' in the name are coded as 2 twice since a vowel lies inbetween them). "Pfister" yields "P236" not "P123" (the first two letters have the same number and are coded once as 'P').

Soundex variants

A similar algorithm called "Reverse Soundex" prefixes the last letter of the name instead of the first.

The NYSIIS algorithm was introduced by the New York State Identification and Intelligence System in 1970 as an improvement to the Soundex algorithm. NYSIIS handles some multi-character n-grams and maintains relative vowel positioning, whereas Soundex does not.

Daitch–Mokotoff Soundex (D–M Soundex) was developed in 1985 by genealogist Gary Mokotoff and later improved by genealogist Randy Daitch because of problems they encountered while trying to apply the Russell Soundex to Jews with Germanic or Slavic surnames (such as Moskowitz vs. Moskovitz or Levine vs. Lewin). D–M Soundex is sometimes referred to as "Jewish Soundex" or "Eastern European Soundex",^[8] although the authors discourage the use of these nicknames. The D–M Soundex algorithm can return as many as 32 individual phonetic encodings for a single name. Results of D-M Soundex are returned in an all-numeric format between 100000 and 999999. This algorithm is much more complex than Russell Soundex.

As a response to deficiencies in the Soundex algorithm, Lawrence Philips developed the Metaphone algorithm in 1990 for the same purpose. 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.

See also

• Phonetic algorithm
• Metaphone
• New York State Identification and Intelligence System
• Match Rating Approach

References

External links

• The Soundex Indexing System (U.S. National Archives and Records Administration)

Ready-to-use soundex converters

• Eastman's Online Genealogy Newsletter Online soundex converter
• van der Harg - Geanealogie: Soundex Dutch soundex converter
• Indic Soundex Converts from all indian languages and English (developed by the Swatantra Malyalam Group)

Programming algorithms for soundex

• Soundex on Rosetta Code Implementations in around twenty languages.
• Text::Soundex Perl module from CPAN
• PHP soundex function
• SimMetrics an open source (sourceforge) library of similarity metrics including a number of soundex variants
• Soundex in C#
• Soundex in Haskell
• Soundex in Java
• Soundex in JavaScript (wrong: prefixes like "van der" are not excluded, original has two soundex codes for names with prefixes)
• Soundex in JavaScript (view page source for code) (wrong: fails if first letter doubled, or vowel separates 2 similar letters)
• Soundex in Ruby
• Soundex in Python
• Soundex in STATA

• Soundex in PostgreSQL
• Soundex Tcl package from the tcllib library

• Indic Soundex's Source Code^{[dead link]} Code for above example.