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morphy - discussion of WordNet's morphological processing
Although only base forms of words are usually stored in WordNet, searches
may be done on inflected forms. A set of morphology functions, 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 intelligent 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.
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" |
| VERB | "ed"
| "" |
| VERB | "ing" | "e" |
| VERB | "ing" | "" |
| ADJ | "er" | "" |
| ADJ | "est"
| "" |
| ADJ | "er" | "e" |
| ADJ | "est" | "e" |
There is one
exception list file for each syntactic category. The exception lists contain
the morphological transformations for strings that are not regular and
therefore cannot be processed in an algorithmic 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 detachment
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 of speech.
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 collocation 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 determines
whether a verb collocation includes a preposition. If it does, a function
is called to try to find the base form in the following manner. 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 database search would
be performed with ask for it , which is found in WordNet, and therefore
returned from Morphy. If a verb collocation does not contain a preposition,
then the base form of each word in the collocation 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 delimiters. It also looks for periods in strings and removes
them if an exact match is not found. A search for an abbreviation like
oct. return the synset for { October, Oct } . Not every pattern of hyphenated
and collocated string is searched for properly, so it may be advantageous
to specify several search strings if the results of a search attempt seem
incomplete.
Morphy contains
code that searches for nouns ending with ful and performs a transformation
on the substring preceeding it. It then appends 'ful' back onto the resulting
string and returns it. For example, if passed the nouns boxesful , it will
return boxful .
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 .
- WNHOME
- Base directory for WordNet. Default is /usr/local/WordNet-3.0 .
- WNSEARCHDIR
- Directory in which the WordNet database has been installed. Default
is WNHOME/dict .
- HKEY_LOCAL_MACHINE\SOFTWARE\WordNet\3.0\WNHome
- Base directory for WordNet. Default is C:\Program Files\WordNet\3.0 .
- pos .exc
- morphology exception lists
wn(1WN)
, wnb(1WN)
, binsrch(3WN)
,
morph(3WN)
, wndb(5WN)
, wninput(7WN)
.
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