Linguistic Objects in this Course Grouping Words PA154 Jazykové modelování (11.1) Pavel Rychlý pary@fi.muni.cz May 11, 2021 Trees (with strings at the nodes) Syntax, semantics ► Algorithms: Gt Sequences (of strings) ► n-grams, tag sequences ► morpheme sequences, phoneme sequences ► Algorithms: Fi "Atoms"(unanalyzed strings) ► Words, morphemes ► Represent by contexts - other words they occur with ► Algorithms: Group PA154 Jazykové modelování (11.1) A Concordance for "party" - from www.webcorp.org.uk A Concordance for "party" - from www.webcorp.org.uk Concordance the web in real-time. Search Wordlist Tool User Guide WebCorp LSE Publications Feedback WebCorp _ive lets you access the Web as a corpus - a large collection of texts from which examples of real language use can be extracted. More Case Insensitive: Span: | 50 characters » | Search API: Google 7] Language: | Not specified Advanced Options thing. She was talking at a party thrown at Daphne's restaurant in have turned it into the hot dinner-party topic. The comedy is the selection for the World Cup party, which will be announced on May 1 in the 1983 general election for a party which, when it could not bear to to attack the Scottish National Party, who look set to seize Perth and that had been passed to a second party who made a financial decision the by-pass there will be a street party. "Then,"he says, "we are going number-crunchers within the Labour party, there now seems little doubt political tradition and the same party. They are both relatively Anglophilic he told Tony Blair's modernised party they must not retreat into "warm " Oh no, I'm just here for the party,"they said. " I think it's terrible A future obliges each party to the contract to fulfil it by be signed by or on behalf of each party to the contract." Mr David N PA154 Jazykové modelovaní (11.1) What Good are Word Senses? What Good are Word Senses? thing. She was talking at a party thrown at Daphne's restaurant in have turned it into the hot dinner-party topic. The comedy is the selection for the World Cup party, which will be announced on May 1 in the 1983 general election for a party which, when it could not bear to to attack the Scottish National Party, who look set to seize Perth and that had been passed to a second party who made a financial decision the by-pass there will be a street party. "Then,"he says, "we are going number-crunchers within the Labour party, there now seems little doubt political tradition and the same party. They are both relatively Anglophilic he told Tony Blair's modernised party they must not retreat into "warm "Oh no, I'm just here for the party,"they said. "I think it's terrible A future obliges each party to the contract to fulfil it by be signed by or on behalf of each party to the contract." Mr David N thing. She was talking at a party thrown at Daphne's restaurant in have turned it into the hot dinner-party topic. The comedy is the selection for the World Cup party, which will be announced on May 1 the by-pass there will be a street party. "Then,"he says, "we are going " Oh no, I'm just here for the party,"they said. " I think it's terrible in the 1983 general election for a party which, when it could not bear to to attack the Scottish National Party, who look set to seize Perth and number-crunchers within the Labour party, there now seems little doubt political tradition and the same party. They are both relatively Anglophilic he told Tony Blair's modernised party they must not retreat into "warm that had been passed to a second party who made a financial decision A future obliges each party to the contract to fulfil it by be signed by or on behalf of each party to the contract." Mr David N PA154 Jazykové modelovaní (11.1) Grouping Words What Good are Word Senses? What Good are Word Senses? John threw a "rain forest" party last December. His living room was full of plants and his box was playing Brazilian music ... Replace word w with sense s Q Splits w into senses: distinguishes this token of w from tokens with sense t B Groups w with other words: groups this token of w with tokens of x that also have sense s PA154 Jazykové modelování (11.1) What Good are Word Senses? What Good are Word Senses? number-crunchers within the Labour party, there now seems little doubt political tradition and the same party. They are both relatively Anglophilic he told Tony Blair's modernised party they must not retreat into "warm thing. She was talking at a party thrown at Daphne's restaurant in have turned it into the hot dinner-party topic. The comedy is the selection for the World Cup Party, which will be announced on May 1 the by-pass there will be a street party. "Then,"he says, "we are going "Oh no, I'm just here for the party,"they said. "I think it's terrible an appearance at the annual awards bash , but feels in no fit state to -known families at a fundraising bash on Thursday night for Learning Who was paying for the bash? The only clue was the name Asprey, Mail, always hosted the annual bash for the Scottish Labour front-popular. Their method is to bash sense into criminals with a short, just cut off people's heads and bash their brains out over the floor, number-crunchers within the Labour party, there now seems little doubt political tradition and the same party. They are both relatively Anglophilic he told Tony Blair's modernised party they must not retreat into "warm thing. She was talking at a party thrown at Daphne's restaurant in have turned it into the hot dinner-party topic. The comedy is the selection for the World Cup party, which will be announced on May 1 the by-pass there will be a street party. "Then,"he says, "we are going "Oh no", I'm just here for the party," they said. "I think it's terrible an appearance at the annual awards bash, but feels in no fit state to -known families at a fundraising bash on Thursday night for Learning Who was paying for the bash? The only clue was the name Asprey, Mail, always hosted the annual bash for the Scottish Labour front-popular. Their method is to bash sense into criminals with a short, just cut off people's heads and bash their brains out over the floor, Grouping Words PA154 Jazykové modelování (11.1) What Good are Word Senses? Cues to Word Sense Semantics / Text understanding ► Axioms about TRANSFER apply to (some tokens of) throw ► Axioms about BUILDING apply to (some tokens of) bank Machine translation Info retrieval / Question answering / Text categ. ► Query or pattern might not match document exactly Backoff for just about anything ► what word comes next? (speech recognition, language ID,...) ► trigrams are sparse but tri-meanings might not be ► bilexical PCFGs: ► p(S[devour] -> NP[lion] VP[devour] | S[devour]) ► approximate by p(S[EAT] -> NP[lion] VP[EAT] | S[EAT]) Speaker's real intention is senses; words are a noisy channel Adjacent words (or their senses) Grammatically related words (subject, object, ...) Other nearby words Topic of document Sense of other tokens of the word in the same document PA154 Jazykové modelování (11.1) Word Classes by Tagging Word Classes by Tagging Every tag is a kind of class Tagger assigns a class to each word token big ram 1 c model I ->t3 PN Verb Det Noun Prep Noun Prep Bill directed a cortege of autos through! Every tag is a kind of class Tagger assigns a class to each word token ► Simultaneously groups and splits words ► "party" gets split into N and V senses ► "bash" gets split into N and V senses ► {party/N, bash/N} vs. {party/V, bash/V} ► What good are these groupings? PA154 Jazykové modelování (11.1) Learning Word Classes Words and Vectors Every tag is a kind of class Tagger assigns a class to each word token ► {party/N, bash/N} vs. {party/V, bash/V} ► What good are these groupings? Good for predicting next word or its class! Role of forward-backward algorithm? ► It adjusts classes etc. in order to predict sequence of words better (with lower perplexity) Represent each word type w (party) by a point in k-dimensional space ► e.g., k is size of vocabulary ► the 17th coordinate of w represents strength of w's association with vocabulary word 17 PA154 Jazykové modelování (11.1) Word aardvark abacus abandoned abbot abduct above zygote zymurgy Count 0 0 3 1 0 7 1 0 too high too low is: Jim Jeffords abandoned the Republican party. There were lots of abbots and nuns dancing at that party. The party above the art gallery was, above all, a laboratory for synthesizing zygotes and beer. Represent each word type w (party) by a point in k-dimensional space ► e.g., k is size of vocabulary ► the 17th coordinate of w represents strength of w's association with vocabulary word 17. How might you measure this? ► how often words appear next to each other ► how often words appear near each other ► how often words are syntactically linked should correct for commonness of word (e.g., "above") PA154 Jazykové modelování (11.1) Learning Classes by Clustering Represent each word type w (party) by a point in k-dimensional space ► e.g., k is size of vocabulary ► the 17th coordinate of w represents strength of w's association with vocabulary word 17. Plot all word types in k-dimensional space Look for clusters of close-together types Plot all word types in k-dimensional space Look for clusters of close-together types Plot in k dimensions (k—3) Grouping Words PA154 Jazykové modelování (11.1) Grouping Words Bottom-Up Clustering Single-Link Start with one cluster per point Repeatedly merge 2 closest clusters ► Single-link: dist(A.B) = min dist(a.b) for a G A, b G B ► Complete-link: dist(A.B) = max dist(a.b) for a G A, b G B earľli word type ts 3 single-puinT duster Again, merge closest pair of clusters: ► Single-link: clusters are close if any of their points are dist(A.B) = min dist(a.b) for a G A,b G B Grouping Words PA154 Jazykové modelování (11.1) Grouping Words Single-Link Complete-Link Fast, but tend to get long, stringy, meandering clusters Again, merge closest pair of clusters: ► Complete-link: clusters are close only if all of their points are dist(A.B) = max dist(a.b) for a G A, b G B PA154 Jazykové modelování (11.1) Complete-Link Summary ■ Slow to find closest pair - need quadratically many distances ■ Start with one cluster per point ■ Repeatedly merge 2 closest clusters ► Single-link: dist(A.B) = min dist(a.b) for a G A, b G B ► Complete-link: dist(A.B) = max dist(a.b) for a G A, b G B *■ too slow to update cluster distances after each merge; but alternatives! ► Average-link: dist(A.B) = mean dist(a.b) for a G A, b G B ► Centroid-link: dist(A.B) = dist(mean(A),mean(B)) ■ Stop when clusters are "big enough" ► e.g., provide adequate support for backoff (on a development corpus) ■ Some flexibility in defining dist(a.b) ► Might not be Euclidean distance; e.g., use vector angle Grouping Words 25/27 Grouping Words 26/27 EM Clustering (for k clusters) ■ EM algorithm ► Viterbi version - called "k-means clustering" ► Full EM version - called "Gaussian mixtures" ■ Expectation step: Use current parameters (and observations) to reconstruct hidden structure ■ Maximization step: Use that hidden structure (and observations) to reestimate parameters ■ Parameters: k points representing cluster centers ■ Hidden structure: for each data point (word type), which center generated it? Grouping Words 27/27