Soundex

Soundex is a phonetic algorithm designed to encode words, particularly proper nouns, in order to group those that sound similar despite having different spellings.

The goal is to improve approximate search, phonetic indexing, and the detection of spelling variants in databases.

Soundex generates a key consisting of a letter followed by three digits by following these rules:

— Keep the first letter of the word

— Convert the remaining consonants into numeric codes according to phonetic groups : BFPV=1, CGJKQSXZ=2, DT=3, L=4, MN=5, R=6

— Remove vowels (except the first letter), H, and W

— Merge consecutive identical codes

— Truncate or pad with zeros to obtain a final length of four characters

There is no inverse Soundex algorithm. To find a word from a key, compare that key with the keys of words in a dictionary or database.

Words sharing the same key are considered phonetically similar.

Soundex has several limitations:

— Sensitivity to the first letter

— Poor adaptation for non-English languages

— Overly broad groupings, generating false positives

— Lack of precision for short or atypical names

Identify a Soundex key by its typical structure: a capital letter followed by three numbers between 0 and 6

The first letter corresponds literally to the letter of the original word, while the numbers encode the consonantal sounds.

Several derivatives exist:

— American Soundex: classic version, used in many historical systems.

— Metaphone / Double Metaphone: more modern and precise alternatives, often preferred in contemporary systems.

Soundex was formalized at the beginning of the 20th century, particularly in the context of census work in the United States, around the years 1910–1920, to facilitate the search for surnames despite their often variable spellings.