With the help of Dennis Grinberg and John Lafferty, we have now released
version 2, which is significantly better than version 1. Some of the
advantages are described below. We have also created a web site about
the system:
http://bobo.link.cs.cmu.edu/grammar/html/intro.html
This site contains a lot of information about the parser, and allows you
to experiment with it. The parser and its documentation are available
via anonymous ftp:
/afs/cs/user/sleator/public/link-grammar on host ftp.cs.cmu.edu
We think the parser could now be useful for a variety of applications
that involve recovering the syntactic structure of text. These might
include speech recognition, speech generation, grammar checking, machine
translation, and language understanding systems.
P.S. This message was sent to a mailing list consisting of 1230 people
who (1) have expressed interest in our work (as determined by a crude
analysis of our email, and other correspondence), or (2) are on mailing
lists whose subjects would indicate interest in this work. We have
attempted to eliminate all duplicates form the list. We apologize if
you receive this message twice, or if this information is of not of
interest to you.
Davy Temperley Daniel Sleator
......................................................................
Daniel Sleator Office: 412-268-7563
Professor of Computer Science Fax: 412-268-5576
Carnegie Mellon University Home: 412-362-8675
Pittsburgh, PA 15213 sleator@cs.cmu.edu
IMPROVEMENTS
1. The new version is "robust". The old version could not assign any
syntactic structure to a sentence unless it could completely
interpret the sentence. The new version is able to skip over portions
of the sentence that it cannot understand, and assign some structure
to the rest of the sentence.
2. Quite apart from the "robustness" feature, the parser's coverage is
vastly improved. The old system could only fully parse about 30% of
sentences in a typical Wall Street Journal article. The new version
can find complete parses for 70-75% of such sentences.
3. The new version has a much larger dictionary. The old version had
about 25000 words; the new version has about 59000. (Here we count
individual forms of verbs and nouns: e.g., "chase", "chases",
"chased", and "chasing" are counted as separate words. The number of
"stem" words is probably about 30000.)
4. The new version has an "unknown word" feature. It has a general
syntactic category which it assigns to any word which it does not
recognize. (In the process, it labels the unknown word as a noun,
verb, adjective, or adverb.)
5. The parser has a "two-stage" system. At the first stage, it considers
common syntactic constructions; the "stage one" coverage is roughly
comparable to the coverage of the earlier version. In the second
stage, it considers many less common constructions. Here are a few
examples of "stage-two" constructions:
Plural nouns acting as noun modifiers ("He was booked on a weapons
violations charge")
Adjectival nouns preceding adjectives ("City clerical workers went on
strike today")
Prepositional phrases modifying verbs, but preceding the direct object
("She sold for five dollars the ring her mother gave her").
Manner adverbs modifying adjectives ("The delicately quiet tone of the
cello blended well with the fiercely percussive piano chords")
Unusual cases of subject-verb inversion ("Also invited to the meeting
were several prominent scientists")
Auxiliaries without main verbs ("If you don't want to do it, you
should find someone who will")
Unusual uses of gerunds ("We have to talk about this sleeping in class
and girl chasing")
Noun-phrases introducing proper names ("The actress Whoopi Goldberg
and the singer Michael Jackson attended the ceremony")
Hyphenated expressions as noun-phrases ("The buy-out caused a
free-for-all in the mid-afternoon")
6. The post-processing system released with the earlier version has been
improved. There is now a "wild-card" character for post-processing,
allowing rules to be expressed much more parsimoniously.
7. The new version has greatly improved documentation. We have compiled
a "guide-to-links", describing every connector type and every
syntactic construction covered by the parser. The guide also contains
a complete description of post-processing. We also provide a general
introduction (in a file called "manual") to the system, describing
the general logic of link grammars and the post-processing system and
the notational system we use for expressing them, as well as a number
of special features of the parser. We hope this will allow people
to modify the system substantially if they wish or design their own
versions (e.g. dictionaries for other languages).
8. The dictionary is using a different (and much more logical) link
naming scheme.