A method for training a machine learning model for open domain question answering includes receiving trained classifiers for question answering. The received trained classifiers are used to generate a set of candidate answers to a question. Second trained classifiers are used for scoring each of the candidate answers. The scoring indicates a measure of how well each candidate answer answers the question. Using the second trained classifiers for scoring each of the candidate answers includes comparing each candidate answer to a first ground truth corresponding to the question. A set of top-scoring candidate answers is presented to a human operator who marks each as correct or incorrect. The correct candidate answers are treated as additional ground truths for further training the first trained classifiers.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A method for training a machine learning model for open domain question answering, comprising: receiving one or more first trained classifiers for question answering; using the received one or more trained classifiers to generate a set of candidate answers to a question; using one or more second trained classifiers for scoring each of the candidate answers, wherein the scoring indicates a measure of how well each candidate answer answers the question, and wherein using the second trained classifiers for scoring each of the candidate answers includes comparing each candidate answer to a first ground truth corresponding to the question; presenting a set of top-scoring candidate answers to a human operator; receiving an indication from the human operator as to whether each presented candidate answer is a correct answer for the question or an incorrect answer for the question; treating the candidate answers indicated as correct by the human operator as an additional ground truth for the question; and using the additional ground truth for the question to further train the first trained classifiers. 2. The method of claim 1, wherein the received one or more first trained classifiers were trained using machine learning. 3. The method of claim 2, wherein the received one or more first trained classifiers were trained using the question and the first ground truth as training data. 4. The method of claim 1, wherein the question and the first ground truth are provided to the human operator when presenting the set of top-scoring candidate answers. 5. The method of claim 1, wherein the one or more second trained classifiers were trained using machine learning. 6. The method of claim 5, further comprising: treating the candidate answers indicated as correct by the human operator as an additional ground truth for the question; and using the additional ground truth for the question to further train the second trained classifiers. 7. The method of claim 1, wherein generating the set of candidate answers to the question includes generating features for the candidate answers and the generated features are used by the second trained classifiers in scoring each of the candidate answers. 8. A method for training a machine learning model for open domain question answering, comprising: receiving one or more first trained classifiers for question answering; using the received one or more trained classifiers to generate a set of candidate answers to a question; using one or more second trained classifiers for scoring each of the candidate answers, wherein the scoring indicates a measure of how well each candidate answer answers the question, and wherein using the second trained classifiers for scoring each of the candidate answers includes comparing each candidate answer to a first ground truth corresponding to the question; designating a set of top-scoring answers as a correct answer for the question; treating the candidate answers designated as correct as additional ground truths for the question; and using the additional ground truths for the question to further train the first trained classifiers. 9. The method of claim 8, wherein the candidate answers designated as correct are only treated as additional ground truths for the question for the purpose of further training the first trained classifiers on one occasion. 10. The method of claim 8, wherein the candidate answers designated as correct are added to a set of ground truths for the question along with the first ground truth for the question so that all subsequent further training of the first trained classifiers make use of the added ground truths. 11. The method of claim 8, wherein the received one or more first trained classifiers were trained using machine learning. 12. The method of claim 11, wherein the received one or more first trained classifiers were trained using the question and the first ground truth as training data. 13. The method of claim 8, wherein the one or more second trained classifiers were trained using machine learning. 14. The method of claim 8, further comprising: treating the candidate answers designated as correct as an additional ground truth for the question; and using the additional ground truth for the question to further train the second trained classifiers. 15. The method of claim 8, wherein generating the set of candidate answers to the question includes generating features for the candidate answers and the generated features are used by the second trained classifiers in scoring each of the candidate answers. 16. A method for training a machine learning model for open domain question answering, comprising: receiving a set of questions and corresponding ground truth answers for each of the questions of the set of questions; training a first trained classifiers for question answering by machine learning using the set of questions and corresponding ground truth answers as training data; selecting one of the received set of questions and applying the first trained classifier to the selected question to produce a set of candidate answers; using one or more second trained classifiers for scoring each of the candidate answers, wherein the scoring indicates a measure of how well each candidate answer answers the selected question, and wherein using the second trained classifiers for scoring each of the candidate answers includes comparing each candidate answer to a first ground truth, of the ground truth answers, that corresponds to the selected question; designating a set of candidate answers as correct answers for the selected question based either on score alone or based on human annotations of a set of top-scoring candidate answers; treating the candidate answers designated as correct as additional ground truths for the question; and using the additional ground truths for the question to further train the first trained classifiers. 17. The method of claim 16, wherein the candidate answers designated as correct are only treated as additional ground truths for the question for the purpose of further training the first trained classifiers on one occasion. 18. The method of claim 16, wherein the candidate answers designated as correct are added to a set of ground truths for the question along with the first ground truth for the question so that all subsequent further training of the first trained classifiers make use of the added ground truths. 19. The method of claim 16, wherein human annotations are obtained by presenting a set of top-scoring candidate answers to a human operator, and receiving an indication from the human operator as to whether each presented candidate answer is a correct answer for the question or an incorrect answer for the question. 20. The method of claim 16, wherein generating the set of candidate answers to the question includes generating features for the candidate answers and the generated features are used by the second trained classifiers in scoring each of the candidate answers.