An Operator for Entity Extraction in MapReduce
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Dictionary-based entity extraction involves finding mentions of dictionary entities in text. Text mentions are often noisy, containing spurious or missing words. Efficient algorithms for detecting approximate entity mentions follow one of two general techniques. The first approach is to build an index on the entities and perform index lookups of document substrings. The second approach recognizes that the number of substrings generated from documents can explode to large numbers, to get around this, they use a filter to prune many such substrings which do not match any dictionary entity and then only verify the remaining substrings if they are entity mentions of dictionary entities, by means of a text join. The choice between the index-based approach and the filter & verification-based approach is a case-to-case decision as the best approach depends on the characteristics of the input entity dictionary, for example frequency of entity mentions. Choosing the right approach for the setting can make a substantial difference in execution time. Making this choice is however non-trivial as there are parameters within each of the approaches that make the space of possible approaches very large. In this paper, we present a cost-based operator for making the choice among execution plans for entity extraction. Since we need to deal with large dictionaries and even larger large datasets, our operator is developed for implementations of MapReduce distributed algorithms.
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