Metaphone

Lawrence Philips redirects here. For the football player, see Lawrence Phillips.

Metaphone is a phonetic algorithm, an algorithm published in 1990 for indexing words by their English pronunciation^[1]. It fundamentally improves on the Soundex algorithm by using information about variations and inconsistencies in English spelling and pronunciation to produce a more accurate encoding, which does a better job of matching words and names which sound similar. As with Soundex, similar sounding words should share the same keys. Metaphone is available as a built-in operator in a number of systems, including later versions of PHP.

The original author later produced a new version of the algorithm, which he named Double Metaphone. Contrary to the original algorithm whose application is limited to English only, this version takes into account spelling peculiarities of a number of other languages. In 2009 Lawrence Philips released a third version, called Metaphone 3, which achieves an accuracy of approximately 99% for English words, non-English words familiar to Americans, and first names and family names commonly found in the United States, having been developed according to modern engineering standards against a test harness of prepared correct encodings.

Procedure

Metaphone codes use the 16 consonant symbols 0BFHJKLMNPRSTWXY.^[2] The '0' represents "th" (as an ASCII approximation of Θ), 'X' represents "sh" or "ch", and the others represent their usual English pronunciations. The vowels AEIOU are also used, but only at the beginning of the code.^[3]

1. Drop duplicate adjacent letters, except for C.
2. If the word begins with 'KN', 'GN', 'PN', 'AE', 'WR', drop the first letter.
3. Drop 'B' if after 'M' at the end of the word.
4. 'C' transforms to 'X' if followed by 'IA' or 'H' (unless in latter case, it is part of '-SCH-', in which case it transforms to 'K'). 'C' transforms to 'S' if followed by 'I', 'E', or 'Y'. Otherwise, 'C' transforms to 'K'.
5. 'D' transforms to 'J' if followed by 'GE', 'GY', or 'GI'. Otherwise, 'D' transforms to 'T'.
6. Drop 'G' if followed by 'H' and 'H' is not at the end or before a vowel. Drop 'G' if followed by 'N' or 'NED' and is at the end.
7. 'G' transforms to 'J' if before 'I', 'E', or 'Y', and it is not in 'GG'. Otherwise, 'G' transforms to 'K'.
8. Drop 'H' if after vowel and not before a vowel.
9. 'CK' transforms to 'K'.
10. 'PH' transforms to 'F'.
11. 'Q' transforms to 'K'.
12. 'S' transforms to 'X' if followed by 'H', 'IO', or 'IA'.
13. 'T' transforms to 'X' if followed by 'IA' or 'IO'. 'TH' transforms to '0'. Drop 'T' if followed by 'CH'.
14. 'V' transforms to 'F'.
15. 'WH' transforms to 'W' if at the beginning. Drop 'W' if not followed by a vowel.
16. 'X' transforms to 'S' if at the beginning. Otherwise, 'X' transforms to 'KS'.
17. Drop 'Y' if not followed by a vowel.
18. 'Z' transforms to 'S'.
19. Drop all vowels unless it is the beginning.

Double Metaphone

The Double Metaphone phonetic encoding algorithm is the second generation of this algorithm. Its implementation was described in the June 2000 issue of C/C++ Users Journal.

It is called "Double" because it can return both a primary and a secondary code for a string; this accounts for some ambiguous cases as well as for multiple variants of surnames with common ancestry. For example, encoding the name "Smith" yields a primary code of SM0 and a secondary code of XMT, while the name "Schmidt" yields a primary code of XMT and a secondary code of SMT--both have XMT in common.

Double Metaphone tries to account for myriad irregularities in English of Slavic, Germanic, Celtic, Greek, French, Italian, Spanish, Chinese, and other origin. Thus it uses a much more complex ruleset for coding than its predecessor; for example, it tests for approximately 100 different contexts of the use of the letter C alone.

Metaphone 3

A professional version was released in October 2009, developed by the same author, Lawrence Philips. Metaphone 3 further improves phonetic encoding of words in the English language, non-English words familiar to Americans, and first names and family names commonly found in the United States.^[4] It improves encoding for for proper names in particular to a considerable extent.^[5] The author claims that in general it improves accuracy for all words from the approximately 89% of Double Metaphone to over 99%. Developers can also now set switches in to code to cause the algorithm to encode Metaphone keys 1) taking non-initial vowels into account, as well as 2) encoding voiced and unvoiced consonants differently. This allows the result set to be more closely focused if the developer finds that the search results include too many words that don't resemble the search term closely enough.^[6] Metaphone 3 is sold as source code in C++, Java and C#.^[7]

See also

• Caverphone
• Soundex
• New York State Identification and Intelligence System
• Match Rating Approach

External links

• Open Source Spell Checker
• Another explanation of the algorithm
• Project to write a formal definition of the algorithm
• "The Double Metaphone Search Algorithm", C/C++ Users Journal, June 2000 (full-text access requires registration)
• The Double Metaphone Search Algorithm, By Lawrence Phillips, June 1, 2000, Dr Dobb's, Original article
• Code project article on double metaphone: http://www.codeproject.com/string/dmetaphone1.asp

Metaphone Implementations

• Metaphone implementation in T-SQL
• Soundex, Metaphone, and Double Metaphone implementation in Java
• Soundex, Metaphone, Caverphone implementation in Python
• Text::Metaphone Perl module from CPAN
• Text::DoubleMetaphone Perl module from CPAN
• OCaml implementation of Double Metaphone
• PHP implementation by Stephen Woodbridge
• PHP implementation
• Ruby implementation included in http://english.rubyforge.org
• Ruby implementation included in http://rubyforge.org/projects/text/
• 4GL implementation by Robert Minter
• CodeProject's article about double metaphone implementations
• FileMaker Pro custom function, requiring FileMaker Pro Advanced to implement
• Spanish Metaphone in PHP (First post), from a comment in the PHP Metaphone Manual Page
• Brazilian Portuguese in C Metaphone for Brazilian Portuguese, in C with PHP and PostgreSQL port.
• natural - javascript (nodejs) natural language toolkit
• Spanish Metaphone in Python

Double Metaphone Implementations

• C++ see: http://web.archive.org/web/20080101012741/http://www.cuj.com/documents/s=8038/cuj0006philips/
• C# see: http://www.codeproject.com/KB/recipes/dmetaphone5.aspx
• Perl see: http://search.cpan.org/dist/Text-DoubleMetaphone/
• PHP see: http://swoodbridge.com/DoubleMetaPhone/ and native, in C: http://pecl.php.net/package/doublemetaphone
• Java see: http://commons.apache.org/codec/userguide.html
• Ruby
  • https://github.com/anjlab/rubyfish
  • http://english.rubyforge.org/
  • http://rubyforge.org/projects/text/
• SQL:
  • MySQL see: see: http://www.atomodo.com/code/double-metaphone
  • PostgreSQL see: http://www.postgresql.org/docs/current/static/fuzzystrmatch.html
  • Transact-SQL see: http://www.sqlmag.com/Articles/ArticleID/26094/pg/1/1.html (full-text access requires subscription)
• Python see: http://www.atomodo.com/code/double-metaphone
• Smalltalk, Squeak, also with SoundEx, see: http://www.squeaksource.com/SoundsLike.html
• Visual Basic see: http://www.snakelegs.org/2008/01/18/double-metaphone-visual-basic-implementation/
  • Visual Basic for Applications see: http://bytes.com/topic/access/answers/192513-metaphone-source-code/

References

1. ^ Hanging on the Metaphone, Lawrence Philips. Computer Language, Vol. 7, No. 12 (December), 1990.
2. ^ http://www.sound-ex.com/alternative_zu_soundex
3. ^ http://www.morfoedro.it/doc.php?n=222&lang=en
4. ^ B P Pande and Prof. H S Dhami. Article: Application of Natural Language Processing Tools in Stemming. International Journal of Computer Applications 27(6):14-19, August 2011. Published by Foundation of Computer Science, New York, USA.
5. ^ Best Faces Forward: A Large-scale Study of People Search in the Enterprise I Guy, S Ur, I Ronen, S Weber… - 2012 - http://www.research.ibm.com/haifa/dept/imt/papers/guyCHI12.pdf
6. ^ http://aspell.net/metaphone/
7. ^ http://www.amorphics.com/