Although only base forms of words are usually stored in WordNet,
searches may be done on inflected forms. A set of morphology func-
tions, Morphy, is applied to the search string to generate a form that
is present in WordNet.
Morphology in WordNet uses two types of processes to try to convert the
string passed into one that can be found in the WordNet database.
There are lists of inflectional endings, based on syntactic category,
that can be detached from individual words in an attempt to find a form
of the word that is in WordNet. There are also exception list files,
one for each syntactic category, in which a search for an inflected
form is done. Morphy tries to use these two processes in an intelli-
gent manner to translate the string passed to the base form found in
WordNet. Morphy first checks for exceptions, then uses the rules of
detachment. The Morphy functions are not independent from WordNet.
After each transformation, WordNet is searched for the resulting string
in the syntactic category specified.
The Morphy functions are passed a string and a syntactic category. A
string is either a single word or a collocation. Since some words,
such as axes can have more than one base form (axe and axis), Morphy
works in the following manner. The first time that Morphy is called
with a specific string, it returns a base form. For each subsequent
call to Morphy made with a NULL string argument, Morphy returns another
base form. Whenever Morphy cannot perform a transformation, whether on
the first call for a word or subsequent calls, NULL is returned. A
transformation to a valid English string will return NULL if the base
form of the string is not in WordNet.
The morphological functions are found in the WordNet library. See
morph(3WN) for information on using these functions.
Rules of Detachment
The following table shows the rules of detachment used by Morphy. If a
word ends with one of the suffixes, it is stripped from the word and
the corresponding ending is added. Then WordNet is searched for the
resulting string. No rules are applicable to adverbs.
POS | Suffix | Ending
NOUN | "s" | ""
NOUN | "ses" | "s"
NOUN | "xes" | "x"
NOUN | "zes" | "z"
NOUN | "ches" | "ch"
NOUN | "shes" | "sh"
NOUN | "men" | "man"
NOUN | "ies" | "y"
VERB | "s" | ""
VERB | "ies" | "y"
VERB | "es" | "e"
VERB | "es" | ""
VERB | "ed" | "e"
that are not regular and therefore cannot be processed in an algorith-
mic manner. Each line of an exception list contains an inflected form
of a word or collocation, followed by one or more base forms. The list
is kept in alphabetical order and a binary search is used to find words
in these lists. See wndb(5WN) for information on the format of the
exception list files.
In general, single words are relatively easy to process. Morphy first
looks for the word in the exception list. If it is found the first
base form is returned. Subsequent calls with a NULL argument return
additional base forms, if present. A NULL is returned when there are
no more base forms of the word.
If the word is not found in the exception list corresponding to the
syntactic category, an algorithmic process using the rules of detach-
ment looks for a matching suffix. If a matching suffix is found, a
corresponding ending is applied (sometimes this ending is a NULL
string, so in effect the suffix is removed from the word), and WordNet
is consulted to see if the resulting word is found in the desired part
As opposed to single words, collocations can be quite difficult to
transform into a base form that is present in WordNet. In general,
only base forms of words, even those comprising collocations, are
stored in WordNet, such as attorney general. Transforming the colloca-
tion attorneys general is then simply a matter of finding the base
forms of the individual words comprising the collocation. This usually
works for nouns, therefore non-conforming nouns, such as customs duty
are presently entered in the noun exception list.
Verb collocations that contain prepositions, such as ask for it, are
more difficult. As with single words, the exception list is searched
first. If the collocation is not found, special code in Morphy deter-
mines whether a verb collocation includes a preposition. If it does, a
function is called to try to find the base form in the following man-
ner. It is assumed that the first word in the collocation is a verb
and that the last word is a noun. The algorithm then builds a search
string with the base forms of the verb and noun, leaving the remainder
of the collocation (usually just the preposition, but more words may be
involved) in the middle. For example, passed asking for it, the data-
base search would be performed with ask for it, which is found in Word-
Net, and therefore returned from Morphy. If a verb collocation does
not contain a preposition, then the base form of each word in the col-
location is found and WordNet is searched for the resulting string.
Hyphenation also presents special difficulties when searching WordNet.
It is often a subjective decision as to whether a word is hyphenated,
joined as one word, or is a collocation of several words, and which of
the various forms are entered into WordNet. When Morphy breaks a
string into "words", it looks for both spaces and hyphens as delim-
iters. It also looks for periods in strings and removes them if an
Since many noun collocations contains prepositions, such as
line of products, an algorithm similar to that used for verbs should be
written for nouns. In the present scheme, if Morphy is passed
lines of products, the search string becomes line of product, which is
not in WordNet
Morphy will allow non-words to be converted to words, if they follow
one of the rules described above. For example, it will happily convert
plantes to plants.
ENVIRONMENT VARIABLES (UNIX)
WNHOME Base directory for WordNet. Default is
WNSEARCHDIR Directory in which the WordNet database has been
installed. Default is WNHOME/dict.
Base directory for WordNet. Default is C:\Pro-
pos.exc morphology exception lists
wn(1WN), wnb(1WN), binsrch(3WN), morph(3WN), wndb(5WN), wninput(7WN).
WordNet 3.0 Dec 2006 MORPHY(7WN)
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