stemmer

information science, human language A program or algorithm

which determines the morphological root of a given inflected

(or, sometimes, derived) word form -- generally a written word

form.

A stemmer for English, for example, should identify the

string "cats" (and possibly "catlike", "catty" etc.) as

based on the root "cat", and "stemmer", "stemming", "stemmed"

as based on "stem".

English stemmers are fairly trivial (with only occasional

problems, such as "dries" being the third-person singular

present form of the verb "dry", "axes" being the plural of

"ax" as well as "axis"); but stemmers become harder to design

as the morphology, orthography, and character encoding of

the target language becomes more complex. For example, an

Italian stemmer is more complex than an English one (because

of more possible verb inflections), a Russian one is more

complex (more possible noun declensions), a Hebrew one is even

more complex (a hairy writing system), and so on.

Stemmers are common elements in query systems, since a user

who runs a query on "daffodils" probably cares about documents

that contain the word "daffodil" (without the s).

(This dictionary has a rudimentary stemmer which currently

(April 1997) handles only conversion of plurals to singulars).

(1997-04-09)