Question Answering of Bar Exams by Paraphrasing and Legal Text Analysis
Our legal question answering system combines legal information retrieval and textual entailment, and exploits paraphrasing and sentence level analysis of queries and legal statutes. We have evaluated our system using the training data from the competition on legal information extraction/entailment (COLIEE) 2016. The competition focuses on the legal information processing required to answer yes/no questions from Japanese legal bar exams, and it consists of three phases: legal ad hoc information retrieval (Phase 1) textual entailment (Phase 2) and a combination of information retrieval and textual entailment (Phase 3) Phase 1 requires the identification of Japan civil law articles relevant to a legal bar exam query. For this phase, we have used an information retrieval approach using TF IDF and a Ranking SVM. Phase 2 requires decision on yes/no answer for previously unseen queries, which we approach by comparing the approximate meanings of queries with relevant articles. Our meaning extraction process uses a selection of features based on a kind of paraphrase, coupled with a condition/conclusion/exception analysis of articles and queries. We also identify synonym relations using word embedding, and detect negation patterns from the articles. Our heuristic selection of attributes is used to build an SVM model, which provides the basis for ranking a decision on the yes/no questions. Experimental evaluation show that our method outperforms previous methods. Our result ranked highest in the Phase 3 in the COLIEE 2016 competition.
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