Natural Language Processing · TEE · papers
Q1d · Ambiguity in NLP
2023-01-30 · re-exam · recovered AI paper
Previous examination · complete worked answers
Answer
Ambiguity means an expression supports more than one interpretation. Good exam answers name the ambiguity and explain both readings.
| Challenge | Example | Why a system can fail |
|---|---|---|
| Lexical/sense ambiguity | bank: finance or river edge | One written word has several senses |
| Syntactic ambiguity | I saw the man with a telescope. | The telescope may modify saw or the man |
| Reference ambiguity | Riya told Neha that she won. | She may refer to either person without more context |
| Sarcasm | Great, another delay. | Literal positive word conveys frustration |
| Negation | The film was not good. | Dropping not reverses meaning |
| Domain shift | “Positive” in a medical report | Meaning/use differs by domain |
| Code mixing | Kal meeting reschedule karna. | Several languages and spelling conventions |
| Noisy text | tmrw, repeated letters, typos | Vocabulary/token boundaries become uncertain |
| Low-resource setting | Few labelled examples in a language | Models lack representative training evidence |
| Bias and privacy | Skewed data or personal details | Errors and harms can persist in deployed systems |
Homophones sound alike but may differ in spelling (pair/pear). Homographs share spelling but can differ in meaning or pronunciation (lead the team / lead metal). These are different dimensions from syntactic ambiguity.
Long-distance dependencies, cultural knowledge, idioms, morphology and multilingual writing systems also complicate processing. For “kick the bucket”, literal word-by-word interpretation can miss the idiomatic meaning. For “The book that the students recommended is useful”, the verb is agrees with book across an intervening phrase.
Exam mein challenge ka naam + ek sentence + dono meanings/actual failure likho.
Structural ambiguity occurs when a sentence has more than one valid parse tree. In “I saw the man with a telescope”, the prepositional phrase “with a telescope” can attach to saw (the instrument I used) or to the man (the man possessing the telescope). The words and their order stay the same, but the grouping changes.
| Reading | Attachment | Meaning |
|---|---|---|
| I [saw the man] [with a telescope] | PP modifies VP | I used a telescope to see the man. |
| I saw [the man with a telescope] | PP modifies NP | The man had a telescope. |
A parser may need context, probabilities or semantic constraints to choose between trees. A plain CFG describes permitted structures but does not itself assign a probability to each tree. Do not invent rule probabilities for an ordinary CFG question.
Lexical ambiguity also matters: book can be a noun or verb. In “Book the flight”, the imperative analysis begins S→VP, followed by VP→V NP. A parser that initially chooses book as a noun may reach a dead end and must try another permitted analysis.
Yaad rakho: Same words, alag grouping → alag meaning.