Natural Language Processing · TEE · papers

Q2b · Lesk versus Walker and bank disambiguation

2023-12-01 · final · recovered AI paper

Previous examination · complete worked answers

Question. Differentiate Lesk and Walker WSD. Calculate sense scores and disambiguate “bank” in “Money in this bank fetches an interest of 8% per annum.” [10 marks]

Answer

The Walker approach uses thesaurus categories as semantic evidence. Associate each candidate sense with a category. Count or weight context words that support that category. Choose the largest total.

\operatorname{score}(s)=\sum_{w\in C} I(w,\operatorname{category}(s))

$I=1$ if the supplied category mapping says the context word supports the sense, otherwise $I=0$ . The summation symbol means add all those contributions. Weighted questions may replace 1 with a supplied weight. Category membership must be supplied or justified; it is not guessed from word frequency.

Question. Disambiguate bank using Walker scoring. Context words are money, interest, annum, fetch. The finance category supports money, interest and annum; the location category supports none of these words.

Given

Two categories: Finance and Location. Each supported word contributes 1.

To find

The two totals and selected bank sense.

Formula and why it applies

Sum the category indicators for each sense.

Step 1. Make a contribution table

Word	Finance	Location
money	1	0
interest	1	0
annum	1	0
fetch	0	0

Step 2. Add Finance

$1+1+1+0=3$ .

Step 3. Add Location

$0+0+0+0=0$ .

Step 4. Select

3 > 0, so select the financial institution.

Answer. Finance, with score 3 versus 0.

Question. Use Walker scoring for “The fisherman caught bass beside the lake.” Context {fisherman,caught,lake}. The Fish category contains all three clues; the Music category contains none.

Given

Fish and Music senses, binary category membership given.

To find

The correct bass sense.

Formula and why it applies

Score = sum of context-category matches.

Step 1. Record Fish matches

fisherman → 1; caught → 1; lake → 1.

Step 2. Add Fish score

$1+1+1=3$ .

Step 3. Add Music score

$0+0+0=0$ .

Step 4. Choose

Fish has the larger score.

Answer. Bass refers to a fish.

Question. Score “The player used a bat in the match.” Context {player,match}. Sport supports both words with weights 2 and 1; Animal supports neither. Use the supplied weighted Walker scheme.

Given

Sport weights {player:2, match:1}; Animal weights {player:0, match:0}.

To find

Weighted sense scores.

Formula and why it applies

Use the sum of supplied weights, not an unweighted count, because the question explicitly gives weights.

Step 1. Sport contribution of player

Add 2.

Step 2. Sport contribution of match

Add 1. Sport total = 2 + 1 = 3.

Step 3. Animal total

0 + 0 = 0.

Step 4. Compare

3 > 0 selects the sporting implement.

Answer. Bat is the sports implement.

Walker: dictionary ke exact words nahi, context kis topic/category ko support karta hai woh count.

Aspect	Lesk	Walker/thesaurus method
Evidence	Overlap of context with dictionary glosses	Context-word membership in semantic subject categories
Score	Number of shared normalized words	Number/weight of context words supporting each sense category
Dependency	Gloss definitions and preprocessing	Thesaurus categories and their assignments

Given

Context is the printed sentence. No thesaurus category list is supplied.

To find

State the sense and give a transparent illustrative score.

Formula: which one and why

Declare the categories first; count only declared evidence. A numerical Walker score is not uniquely determined without the thesaurus assignments.

Step 1. Choose explicit illustrative categories

Assume money and interest belong to FINANCE; river, water and shore belong to RIVER. Ignore all other tokens as unassigned.

Step 2. Count support

Candidate bank sense	Matching clues	Score
Financial institution	money, interest	2
River edge	none	0

Step 3. Compare

2 > 0, so choose the financial-institution sense under this stated assignment.

Final answer

bank = financial institution. The score 2 versus 0 is conditional on the declared illustrative thesaurus, not supplied numerical data.

Source / convention note. The original gives a sentence but no thesaurus/category mapping, so a unique numerical score cannot be recovered.