Thesauruses for Natural Language Processing
Adam Kilgarriff
Lexicography MasterClass
and
University of Brighton
Outline
Definition Uses for NLP WASPS thesaurus web thesauruses Argument: words not word senses Evaluation proposals Cyborgs
What is a thesaurus?
a resource that groups words according to similarity
Manual and automatic
Manual– Roget, WordNets, many publishers
Automatic– Sparck Jones (1960s), Grefenstette (1994), Lin
(1998), Lee (1999) – aka distributional– two words are similar if they occur in same
contexts
Are they comparable?
Thesauruses in NLP
sparse data
Thesauruses in NLP sparse data
does x go with y?– don’t know, they have never been seen together
New question:does x+friends go with y+friends– indirect evidence for x and y– thesaurus tells us who friends are– “backing off”
Relevant in:
Parsing– PP-attachment– conjunction scope
Bridging anaphors Text cohesion Word sense disambiguation (WSD) Speech understanding Spelling correction
Speech understanding
He’s as headstrong as an alleg***** in the upwaters of the Yangtze
Speech understanding
He’s as headstrong as an alleg***** in the upwaters of the Yangtze
allegory?
Speech understanding
He’s as headstrong as an alleg***** in the upwaters of the Yangtze
allegory? alligator?
Speech understanding
He’s as headstrong as an alleg***** in the upwaters of the Yangtze
allegory? in upwaters? No alligator? in upwaters? No
Speech understanding
He’s as headstrong as an alleg***** in the upwaters of the Yangtze
allegory? in upwaters? No alligator? in upwaters? No allegory+friends in upwaters? No alligator+friends in upwaters? Yes
PP-attachmentinvestigate stromatolite with microscope/speckles
– microscope: verb attachment– speckles: noun attachment
inspect jasper with spectrometer– which?
PP attachment (cont)
compare frequencies of– <inspect, with, spectrometer>– <jasper, with, spectrometer>
PP attachment (cont)
compare frequencies of– <inspect, with, spectrometer>– <jasper, with, spectrometer>
both zero? Try– <inspect+friends, with,
spectrometer+friends>– <jasper+friends, with,
spectrometer+friends>
Conjunction scope
Compare– old boots and shoes– old boots and apples
Conjunction scope
Compare– old boots and shoes– old boots and apples
Are the shoes old?
Conjunction scope
Compare– old boots and shoes– old boots and apples
Are the shoes old? Are the apples old?
Conjunction scope
Compare– old boots and shoes– old boots and apples
Are the shoes old? Are the apples old? Hypothesis:
– wide scope only when words are similar
Conjunction scope
Compare– old boots and shoes– old boots and apples
Are the shoes old? Are the apples old? Hypothesis:
– wide scope only when words are similar hard problem: thesaurus might help
Bridging anaphor resolution
– Maria bought a large apple. The fruit was red and crisp.
fruit and apple co-refer
Bridging anaphor resolution
– Maria bought a large apple. The fruit was red and crisp.
fruit and apple co-refer How to find co-referring terms?
Text cohesion
words on same theme– same segment
change in theme of words– new segment
same theme: same thesaurus class
Word Sense Disambiguation (WSD) pike: fish or weapon
– We caught a pike this afternoon probably no direct evidence for
– catch pike probably is direct evidence for
– catch {pike,carp,bream,cod,haddock,…}
WordNet, Roget
widely used for all the above
The WASPS thesaurus– credit: David Tugwell– EPSRC grant K8931
POS-tag, lemmatise and parse the BNC (100M words)
Find all grammatical relations– <obj, climb, bank>– <modifier, big, bank>– <subject, bank, refuse>
70 million triples
WASPS thesaurus (cont)
Similarity:– <obj, drink, beer>– <obj, drink, wine>
one point similarity between beer and wine count all points of similarity between all pairs
of words weight according to frequencies
– product of MI: Lin (1998)
Word Sketches
one-page summary of a word’s grammatical and collocational behaviour
demo: http://wasps.itri.bton.ac.uk the Sketch Engine
– input any corpus– generate word sketches and thesaurus– just available now
Nearest neighbours to zebra
Nearest neighbours
zebra: giraffe buffalo hippopotamus rhinoceros gazelle antelope cheetah hippo leopard kangaroo crocodile deer rhino herbivore tortoise primate hyena camel scorpion macaque elephant mammoth alligator carnivore squirrel tiger newt chimpanzee monkey
exception: exemption limitation exclusion instance modification restriction recognition extension contrast addition refusal example clause indication definition error restraint reference objection consideration concession distinction variation occurrence anomaly offence jurisdiction implication analogy
pot: bowl pan jar container dish jug mug tin tub tray bag saucepan bottle basket bucket vase plate kettle teapot glass spoon soup box can cake tea packet pipe cup
VERBS
measure
determine assess calculate decrease monitor increase evaluate reduce detect estimate indicate analyse exceed vary test observe define record reflect affect obtain generate predict enhance alter examine quantify relate adjust
boil
simmer heat cook fry bubble cool stir warm steam sizzle bake flavour spill soak roast taste pour dry wash chop melt freeze scald consume burn mix ferment scorch soften
ADJECTIVES
hypnotic
haunting piercing expressionless dreamy monotonous seductive meditative emotive comforting expressive mournful healing indistinct unforgettable unreadable harmonic prophetic steely sensuous soothing malevolent irresistible restful insidious expectant demonic incessant inhuman spooky
pink
purple yellow red blue white pale brown green grey coloured bright scarlet orange cream black crimson thick soft dark striped thin golden faded matching embroidered silver warm mauve damp
Nearest neighbours
crane winch swan heron
winch crane heron tern
heron mast crane gull
tractor rigging gull swan
truck pump tern crane
swan tractor curlew flamingo
no clustering (tho’ could be done) no hierarchy (tho’ could be done) rhythm all on the web: http://wasps.itri.bton.ac.
uk– registration required
The web
an enormous linguist’s playground– Computational Linguistics Special Issue,
Kilgarriff and Grefenstette (eds) 29 (3)• (coming soon)
Google sets
http://labs.google.com/sets Input: zebra giraffe buffalo
Google sets
http://labs.google.com/sets Input: zebra giraffe buffalo kudu hyena impala leopard hippo
waterbuck elephant cheetah eland
Google sets
http://labs.google.com/sets Input: harbin beijing nanking
Google sets
http://labs.google.com/sets Input: harbin beijing nanking Output: shanghai chengdu guangzhou
hangzhou changchun zhejiang kunming dalian jinan fuzhou
Tree structure Roget
– all human knowledge as tree structure
– 1000 top categories• subdivisions
– like this» etc» etc
Directories and thesauruses
Yahoo, http://www.yahoo.com Open directory project, http://dmoz.org
– all human activity as tree structure
plus corpus at every node– gather corpus, identify domain vocabulary
• Gonzalo and colleagues, Madrid, CL Special Issue
• Agirre and colleagues, ‘topic signatures’
Words and word senses
automatic thesauruses– words
Words and word senses
automatic thesauruses– words
manual thesauruses– simple hierarchy is appealing– homonyms
Words and word senses
automatic thesauruses– words
manual thesauruses– simple hierarchy is appealing– homonyms– “aha! objects must be word senses”
Problems
Theoretical Practical
Theoretical
Wittgenstein
Don’t ask for the meaning, ask for the use
Practical
Problems
Practical– a thesaurus is a tool– if the tool organises words senses you must do
WSD before you can use it– WSD: state of the art, optimal conditions: 80%
.
Problems
Practical– a thesaurus is a tool– if the tool organises words senses you must do
WSD before you can use it– WSD: state of the art, optimal conditions: 80%
“To use this tool, first replace one fifth of your input with junk”
Avoid word senses
Avoid word senses
This word has three meanings/senses
Avoid word senses
This word has three meanings/senses This word has three kinds of use
– well founded– empirical– we can study it
sorry, roget
sorry, AI
sorry, AI AI model for NLP:
– NLP turns text into meanings– AI reasons over meanings– word meanings are concepts in an ontology– a Roget-like thesaurus is (to a good
approximation) an ontology– Guarino: “cleansing” WordNet
If a thesaurus groups words in their various uses (not meanings)– not the sort of thing AI can reason over
sorry, AI
“linguistics expressions prompt for meanings rather than express meanings”– Fauconnier and Turner 2003
It would be nice if … But …
Evaluation
manual thesauruses– not done
automatic thesauruses: attempts– pseudo-disambiguation (Lee 1999)– with ref to manual ones (Lin 1998)
Task-based evaluation
Task-based evaluation
Parsing– PP-attachment– conjunction scope
Bridging anaphors Text cohesion Word sense disambiguation (WSD) Speech understanding Spelling correction
What is performance at the task– with no thesaurus– with Roget– with WordNet– with WASPS
Plans
set up evaluation tasks theseval web-based thesaurus
– Open Directory Project hierarchies campaign
Cyborgs
Robots: will they take over? Rod Brooks’s answer:
– Wrong question: greatest advances are in what the human+computer ensemble can do
Cyborgs
A creature that is partly human and partly machine – Macmillan English Dictionary
Cyborgs and the Information Society
The thedsaurus-making agent is part human (for precision), part computer (for recall).
Summary: Thesauruses for NLP
Definition Uses for NLP WASPS thesaurus web thesauruses Argument: words not word senses Evaluation proposals Cyborgs
Thesaurus-makers of the future?
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