Natural Language Processing · TEE · papers

Q1b · Lesk WSD

2025-02-21 · re-exam · recovered AI paper

Previous examination · complete worked answers

Question. Discuss Lesk word-sense disambiguation with a suitable example. [individual allocation not printed; Q1 totals 20]

Answer

Lesk is a knowledge-based WSD method that chooses senses whose dictionary descriptions have the greatest overlap with contextual evidence. Original Lesk compares definitions of neighbouring words' senses. A common simplified version compares each target-sense gloss directly with the sentence context. State which version you use.

Simplified Lesk procedure

  1. Remove the target word from the context; tokenize and normalize the remaining content words.
  2. Obtain the gloss for each candidate sense and apply the same normalization.
  3. Count shared words between the context and each gloss.
  4. Select the sense with maximum overlap. If scores tie, report the tie or use a specified tie-break rule.
\operatorname{score}(s)=|C\cap G_s|,\qquad s^*=\arg\max_s\operatorname{score}(s)LaTeX: \operatorname{score}(s)=|C\cap G_s|,\qquad s^*=\arg\max_s\operatorname{score}(s)

CLaTeX: C is the set of context words, G_sLaTeX: G_s the set of words in sense sLaTeX: s's gloss, \capLaTeX: \cap means common elements, |\cdot|LaTeX: |\cdot| means count, and \arg\maxLaTeX: \arg\max means “the sense giving the largest score”. This version counts unique matching words once.

Question. Use simplified Lesk to disambiguate “bank” in “The river water rose near the bank.” Use C = {river, water, rose, near}; financial gloss = {institution, money, deposit}; river gloss = {land, river, water, edge}.

Given

The normalized context and two gloss sets are given. Count exact shared words.

To find

The score of each sense and the selected meaning.

Formula and why it applies

Use \operatorname{score}(s)=|C\cap G_s|LaTeX: \operatorname{score}(s)=|C\cap G_s| because the task specifies context–gloss overlap.

Step 1. Compare the financial sense

No word occurs in both {river, water, rose, near} and {institution, money, deposit}. Overlap = {}.

Step 2. Count the financial score

\operatorname{score}(F)=0LaTeX: \operatorname{score}(F)=0.

Step 3. Compare the river sense

Shared words are {river, water}. “Rose” and “near” are not in the gloss.

Step 4. Count and select

\operatorname{score}(R)=2LaTeX: \operatorname{score}(R)=2. Since 2>0LaTeX: 2>0, choose the river-edge sense.

Answer. Bank means land beside a river.

Question. Use simplified Lesk for “The dog barked loudly.” Treat barked as bark. Context C = {dog, loudly}; sound gloss = {sharp, cry, dog}; tree gloss = {outer, covering, tree}; ship gloss = {sailing, ship}.

Given

Three glosses and normalized context {dog, loudly}.

To find

Select the sense of bark.

Formula and why it applies

\operatorname{score}(s)=|C\cap G_s|LaTeX: \operatorname{score}(s)=|C\cap G_s|. Lemmatization lets barked match the target lemma bark; it does not create additional overlap words.

Step 1. Sound sense

Intersection = {dog}; score = 1.

Step 2. Tree sense

Intersection = {}; score = 0.

Step 3. Ship sense

Intersection = {}; score = 0.

Step 4. Compare

The sound sense has the unique maximum: 1 > 0.

Answer. Bark is the dog's cry.

Question. Apply definition–definition Lesk to “pine cone”. Pine senses: P1 = {evergreen, tree, needle, leaf}; P2 = {waste, sorrow, illness}. Cone senses: C1 = {solid, shape, circular}; C2 = {fruit, evergreen, tree}.

Given

Two candidate senses for each word. Tokens are already normalized; tree and trees would be reduced to the same form if necessary.

To find

The most compatible pair of senses.

Formula and why it applies

Use |G_{P_i}\cap G_{C_j}|LaTeX: |G_{P_i}\cap G_{C_j}| for every pair because this is original-style gloss–gloss comparison.

Step 1. P1 with C1

No shared word → 0.

Step 2. P1 with C2

Shared {evergreen, tree} → 2.

Step 3. P2 with each cone sense

P2–C1 has no overlap → 0; P2–C2 has no overlap → 0.

Step 4. Choose the best pair

The four scores are 0, 2, 0, 0. Maximum 2 belongs to P1–C2.

Answer. Pine is the evergreen tree; cone is its fruit-like reproductive structure.

Limitations: exact overlap misses synonyms, short glosses may produce zeros, and different preprocessing choices change the score. Extended Lesk may include related synset definitions or longer phrase overlaps; do not silently substitute it for a simple question.

Lesk: context aur dictionary mein common words gino; sabse bada overlap jeeta.