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{
"lesson": "06-named-entity-recognition",
"title": "Named Entity Recognition",
"questions": [
{
"stage": "pre",
"question": "What is BIO tagging?",
"options": [
"Per-token labels: B-TYPE for entity start, I-TYPE for inside, O for outside",
"A binary entity vs non-entity scheme",
"A tokenization style",
"A tree representation of entities"
],
"correct": 0,
"explanation": "BIO turns span extraction into token classification with B/I/O prefixes."
},
{
"stage": "pre",
"question": "Why are rule-based gazetteers brittle in production NER?",
"options": [
"They require GPUs",
"They are slow",
"They have zero coverage on new entities and cannot disambiguate (e.g. Apple fruit vs company)",
"They cannot handle multi-token entities"
],
"correct": 2,
"explanation": "Gazetteers can match known strings but cannot disambiguate sense or generalize to unseen names."
},
{
"stage": "check",
"question": "What is the key advantage of a CRF over an HMM for NER?",
"options": [
"CRFs avoid the Viterbi algorithm",
"CRFs never need training data",
"CRFs are discriminative and can mix arbitrary features (shape, capitalization, neighbors)",
"CRFs are faster"
],
"correct": 2,
"explanation": "CRFs are discriminative and let you condition on rich, overlapping features."
},
{
"stage": "check",
"question": "In a BiLSTM-CRF architecture, what role does the CRF layer play?",
"options": [
"Performs tokenization",
"Enforces valid BIO tag sequences by modeling tag-to-tag transitions on top of LSTM emissions",
"Pretrains the LSTM",
"Replaces embeddings"
],
"correct": 1,
"explanation": "The CRF on top of LSTM features models inter-label dependencies and rules out illegal sequences."
},
{
"stage": "check",
"question": "Why must NER be evaluated with entity-level F1, not token-level F1?",
"options": [
"Entity-level F1 is easier to compute",
"Predicted spans must match true spans exactly; token-level F1 overstates accuracy by counting partial matches",
"Token-level F1 cannot handle BIO",
"Entity-level F1 is required by HuggingFace"
],
"correct": 1,
"explanation": "Span exact-match is the meaningful metric; token-level F1 inflates scores via partial overlap."
},
{
"stage": "post",
"question": "What does aggregation_strategy='simple' do in the HuggingFace NER pipeline?",
"options": [
"Lowercases the output",
"Skips tokenization",
"Merges contiguous B-X and I-X tokens into a single span",
"Returns only the most confident entity"
],
"correct": 2,
"explanation": "It merges contiguous BIO tokens of the same type into span-level entities."
},
{
"stage": "post",
"question": "Why does standard BIO fail on nested entities?",
"options": [
"BIO requires a transformer",
"BIO is a flat per-token scheme and cannot express two overlapping spans of different types",
"BIO cannot represent multi-token entities",
"BIO drops the type label"
],
"correct": 1,
"explanation": "BIO assigns one label per token; nested spans need multi-pass or span-based models."
},
{
"stage": "post",
"question": "When does classical NER (CRF or BiLSTM-CRF) still beat an LLM in 2026?",
"options": [
"On nested entities",
"Whenever the input is in English",
"On open-domain narrative",
"Under tight latency budgets, abundant labels, stable ontologies, or non-generative regulatory constraints"
],
"correct": 3,
"explanation": "Classical NER wins on latency, labeled-data regimes, fixed ontologies, and on-prem constraints."
}
]
}