# Q6B · Hobbs: Ramesh and Shyam Subject: Natural Language Processing Exam: TEE Reader: https://deep-learning-study-room.vercel.app/nlp/#tee/papers/reexam-2026/reexam-2026-q6b Canonical: https://deep-learning-study-room.vercel.app/read/nlp/tee/papers/reexam-2026--reexam-2026-q6b/ Actual re-examination · 9 February 2026 · 100 marks · 3 hours Question. i. Explain Hobbs’ Algorithm for pronoun resolution. State its main steps and limitations. ii. Apply Hobbs’ Algorithm to the sentence: “When Ramesh gave Shyam a book, he smiled.” Identify the antecedent of “he” by showing traversal steps. [10 marks] ### Answer **Hobbs’ algorithm** is a syntax-based pronoun-resolution procedure that searches constituency parse trees in a specified order. It proposes noun phrases as antecedents and filters incompatible candidates, for example by number and gender agreement. **Read the tree labels first:** NP means noun phrase; S means sentence/clause; VP means verb phrase. X is the current NP or S search node, and p is the upward path used to reach it. Breadth-first means shallower nodes before deeper nodes; left-to-right fixes the order at the same depth. An N-bar (N′) node is the noun-centred part of an NP in a parse using that label. ### Complete ordered procedure 1. **Locate the pronoun.** Start at the NP immediately dominating the pronoun: the smallest NP containing it. 2. **Make the first climb.** Move upward to the first NP or S above the starting NP. Call it X and record the path p. 3. **Search initially to the left.** Traverse branches below X to the left of p, breadth-first and left-to-right. Propose an NP only if another NP or S lies between that candidate and X. Check agreement and other applicable constraints for each proposed candidate; accept the first eligible compatible one. 4. **Check the highest sentence.** If X is the highest S and no candidate has been accepted, search previous sentence trees, most recent first. In each, traverse breadth-first and left-to-right and propose NPs. Accept the first eligible compatible candidate; if the available context contains none, report no resolved antecedent. 5. **Otherwise climb again.** Move from X to the next NP or S above it. Make that node the new X and record the new upward path p. 6. **Test a higher NP.** If the new X is an NP, propose X only when p did not pass through its nominal N-bar child. Apply the same compatibility checks. Use the labels in the supplied parse; do not invent a missing N-bar branch. 7. **Search left again.** Traverse the new X’s branches to the left of p, breadth-first and left-to-right, proposing NPs. The extra intervening-NP/S requirement in Step 3 belongs to the initial search. 8. **Search permitted right branches.** If X is an S, traverse branches to the right of p, breadth-first and left-to-right, but do not descend below any NP or S encountered. Propose the encountered eligible NPs and test their compatibility. 9. **Repeat or finish.** Return to Step 4 until a compatible candidate is accepted or the available sentence trees are exhausted. Record the candidate order and why each candidate was accepted or rejected. **Why the initial restriction matters:** in “John saw him”, the subject NP John is directly under the clause S, with no additional NP or S between them. Step 3 therefore does not propose John as the ordinary local antecedent of him. A reflexive such as himself is a different grammatical case. The worked question below shows the specific parse and traversal; selecting an antecedent is not simply choosing the nearest name. ### Given The pronoun he is the subject of the main clause. The preceding subordinate clause is “When Ramesh gave Shyam a book”. Assume the temporal clause attaches to the whole main sentence. ### To find The first suitable antecedent in the left-to-right breadth-first search of the preceding clause. ``` S (main) ← first X ├── SBAR: When │ └── S (embedded) ← intervening S │ ├── NP: Ramesh ← first candidate │ └── VP │ ├── V: gave │ ├── NP: Shyam │ └── NP: a book ├── NP: he ← start └── VP: smiled ``` ### Step 1. Locate the pronoun NP Start at NP “he” and move upward to its S ancestor. Record the path from he. ### Step 2. Search branches before the pronoun The initial when-clause lies to the left of the path. Apply Step 3: its embedded S lies between each of its noun phrases and the main S, so these NPs satisfy the initial intervening-NP/S requirement. Traverse left-to-right and breadth-first. ### Step 3. Propose noun phrases The subject NP Ramesh is encountered before the deeper object NP Shyam and object NP a book. Ramesh agrees with the assumed singular-male pronoun. ### Step 4. Accept the first compatible antecedent Select Ramesh. Shyam is also a semantically possible referent in ordinary discourse, but the algorithm’s stated syntactic preference selects Ramesh first. ### Limitations - Requires a suitable and accurate constituency parse. - Agreement information may be unknown or insufficient when several people match. - Ignores much of the event semantics, discourse focus and world knowledge. - An ambiguous parse or different attachment can change candidate order. **Final answer:** **Ramesh**, under the shown parse and ordinary agreement assumptions. A syntactic preference is not a guarantee about the author’s intended meaning. **Yaad rakho:** Left branches ko breadth-first dekho; pehla eligible matching NP choose karo.