Mining Paraphrases from Self-anchored Web Sentence Fragments

摘要

Near-synonyms or paraphrases are beneficial in a variety of natural language and information retrieval applications, but so far their acquisition has been confined to clean, trustworthy collections of documents with explicit external attributes. When such attributes are available, such as similar time stamps associated to a pair of news articles, previous approaches rely on them as signals of potentially high content overlap between the articles, often embodied in sentences that are only slight, paraphrase-based variations of each other. This paper introduces a new unsupervised method for extracting paraphrases from an information source of completely different nature and scale, namely unstructured text across arbitrary Web textual documents. In this case, no useful external attributes are consistently available for all documents. Instead, the paper introduces linguistically-motivated text anchors, which are identified automatically within the documents. The anchors are instrumental in the derivation of paraphrases through lightweight pairwise alignment of Web sentence fragments. A large set of categorized names, acquired separately from Web documents, serves as a filtering mechanism for improving the quality of the paraphrases. A set of paraphrases extracted from about a billion Web documents is evaluated both manually and through its impact on a natural-language Web search application.