Automated detection of the first document reporting each new event in temporally-sequenced streams of documents is an open challenge. In this paper we propose a new approach which addresses this problem in two stages: 1) using a supervised learning algorithm to classify the on-line document stream into pre-defined broad topic categories, and 2) performing topic-conditioned novelty detection for documents in each topic. We also focus on exploiting named-entities for event-level novelty detection and using feature-based heuristics derived from the topic histories. Evaluating these methods using a set of broadcast news stories, our results show substantial performance gains over the traditional one-level approach to the novelty detection problem.

Confidence annotation allows a spoken dialog system to accurately assess the likelihood of misunderstanding at the utterance level and to avoid breakdowns in interaction. We describe experiments that assess the utility of features from the decoder, parser and dialog levels of processing. We also investigate the effectiveness of various classifiers, including Bayesian Networks, Neural Networks, SVMs, Decision Trees, AdaBoost and Naive Bayes, to combine this information into an utterancelevel confidence metric. We found that a combination of a subset of the features considered produced promising results with several of the classification algorithms considered, e.g., our Bayesian Network classifier produced a 45.7% relative reduction in confidence assessment error and a 29.6% reduction relative to a handcrafted rule.

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