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Published byAlbert Atkinson Modified over 8 years ago
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Dialogue Act Tagging Discourse and Dialogue CMSC 35900-1 November 4, 2004
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Roadmap Maptask overview Coding –Transactions –Games –Moves Assessing agreement
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Maptask Conducted by HCRC – Edinburgh/Glasgow Task structure: –2 participants: Giver, follower –2 slightly different maps Giver guides follower to destination on own map –Forces interaction, ambiguities, disagreements, etc –Conditions: Familiar/not; Visible/not
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Dialogue Tagging Goal: Represent dialogue structure as generically as possible Three level scheme: –Transactions Major subtasks in participants overall task –Conversational Games Correspond to G&S discourse segments –Conversational Moves Initiation and response steps
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Basic Dialogue Moves Initiations and responses Cover acts observed in dialogue – generalized Initiations: Instruct: tell to carry out some action; Explain: give unelicited information; Check: ask for confirmation; Align:check attention; Query-yn: Query-wh Responses:Acknowledge: signal understand & accept; Reply-y; Reply-n; Reply-wh; Clarify Ready:Inter-game moves
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Game Coding Initiation: –Identified by first move Purpose – carry through to completion –May embed other games – Mark level –Mark completion/abandonment
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Interrater Agreement How good is tagging? A tagset? Criterion: How accurate/consistent is it? Stability: –Is the same rater self-consistent? Reproducibility: –Do multiple annotators agree with each other? Accuracy: –How well do coders agree with some “gold standard”?
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Agreement Measure Kippendorf’s Kappa (K) –Applies to classification into discrete categories –Corrects for chance agreement K<0 : agree less than expected by chance –Quality intervals: >= 0.8: Very good; 0.6<K<0.8: Good, etc Maptask: K=0.92 on segmentation, –K = 0.83 on move labels
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Dialogue Act Tagging Other tagsets –DAMSL, SWBD-DAMSL, VERBMOBIL, etc Many common move types –Vary in granularity Number of moves, types Assignment of multiple moves
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Dialogue Act Recognition Goal: Identify dialogue act tag(s) from surface form Challenge: Surface form can be ambiguous –“Can you X?” – yes/no question, or info-request “Flying on the 11t h, at what time?” – check, statement Requires interpretation by hearer –Strategies: Plan inference, cue recognition
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Plan-inference-based Classic AI (BDI) planning framework –Model Belief, Knowledge, Desire Formal definition with predicate calculus –Axiomatization of plans and actions as well –STRIPS-style: Preconditions, Effects, Body –Rules for plan inference Elegant, but.. –Labor-intensive rule, KB, heuristic development –Effectively AI-complete
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Cue-based Interpretation Employs sets of features to identify –Words and collocations: Please -> request –Prosody: Rising pitch -> yes/no question –Conversational structure: prior act Example: Check: Syntax: tag question “,right?” Syntax + prosody: Fragment with rise N-gram: argmax d P(d)P(W|d) –So you, sounds like, etc Details later ….
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Recognizing Maptask Acts Assume: – Word-level transcription – Segmentation into utterances, –Ground truth DA tags Goal: Train classifier for DA tagging –Exploit: Lexical and prosodic cues Sequential dependencies b/t Das –14810 utts, 13 classes
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Features for Classification Acoustic-Prosodic Features: –Pitch, Energy, Duration, Speaking rate Raw and normalized, whole utterance, last 300ms 50 real-valued features Text Features: –Count of Unigram, bi-gram, tri-grams Appear multiple times 10000 features, sparse Features z-score normalized
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Classification with SVMs Support Vector Machines –Create n(n-1)/2 binary classifiers Weight classes by inverse frequency Learn weight vector and bias, classify by sign –Platt scaling to convert outputs to probabilities
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Incorporating Sequential Constraints Some sequences of DA tags more likely: –E.g. P(affirmative after y-n-Q) = 0.5 – P(affirmative after other) = 0.05 Learn P(yi|yi-1) from corpus –Tag sequence probabilities –Platt-scaled SVM outputs are P(y|x) Viterbi decoding to find optimal sequence
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Results SVM OnlySVM+Seq Text Only58.159.1 Prosody Only41.442.5 Text+Prosody61.865.5
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From Human to Computer Conversational agents –Systems that (try to) participate in dialogues –Examples: Directory assistance, travel info, weather, restaurant and navigation info Issues: –Limited understanding: ASR errors, interpretation –Computational costs: broader coverage -> slower, less accurate
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Dialogue Manager Tradeoffs Flexibility vs Simplicity/Predictability –System vs User vs Mixed Initiative –Order of dialogue interaction –Conversational “naturalness” vs Accuracy –Cost of model construction, generalization, learning, etc Models: FST, Frame-based, HMM, BDI Evaluation frameworks
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