Techniques for question answering involve receiving, from a user, a text input expressing a question in natural language. In response to the question, a text output expressing an answer to the question may be generated. A plurality of documents comprising natural language text may be analyzed, involving mapping the question to one or more hypotheses, analyzing at least one passage of text in at least one of the documents to determine whether the passage entails at least one of the hypotheses, and in response to determining that the passage entails at least one of the hypotheses, identifying the passage as providing supporting evidence for the answer to the question. The answer and the at least one passage identified as providing supporting evidence for the answer may be presented to the user in response to the text input.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A method comprising: receiving, from a user, a text input expressing a question in natural language; generating, in response to the question, a text output expressing an answer to the question; analyzing, using a language analysis component implemented via at least one processor, a plurality of documents comprising natural language text, the analyzing comprising: mapping the question to one or more hypotheses, analyzing at least one passage of text in at least one of the plurality of documents to determine whether the at least one passage entails at least one of the one or more hypotheses, and in response to determining that the at least one passage entails at least one of the one or more hypotheses, identifying the at least one passage as providing supporting evidence for the answer to the question; and presenting to the user, in response to the text input, the answer and the at least one passage from the at least one of the documents identified as providing supporting evidence for the answer. 2. The method of claim 1, wherein the analyzing further comprises: scoring passages in at least some of the plurality of documents based at least in part on strength of the passages' supporting evidence for the answer; and selecting one or more of the passages for presentation to the user based on the passages' scores. 3. The method of claim 1, wherein generating the text output expressing the answer comprises determining the answer based at least in part on the text in the at least one passage. 4. The method of claim 3, wherein determining the answer comprises selecting between at least a first answer supported by a first set of one or more passages of text in the plurality of documents and a different second answer supported by a second set of one or more passages of text in the plurality of documents. 5. The method of claim 4, wherein selecting between at least the first answer and the second answer comprises comparing the first and second sets of passages based at least in part on (a) how many documents are represented in the first set of passages versus how many documents are represented in the second set of passages, and/or (b) strength of the first set of passages' supporting evidence for the first answer versus strength of the second set of passages' supporting evidence for the second answer. 6. The method of claim 3, wherein determining the answer comprises: identifying a plurality of constraints posed by the question; matching different constraints of the plurality of constraints to passages in different documents of the plurality of documents; and identifying an answer supported by the passages in combination matched to the plurality of constraints of the question. 7. The method of claim 6, further comprising selecting one or more of the matched passages for presentation to the user based at least in part on how many of the plurality of constraints of the question are matched to the one or more matched passages. 8. At least one computer-readable storage medium storing computer-executable instructions that, when executed, perform a method comprising: receiving, from a user, a text input expressing a question in natural language; generating, in response to the question, a text output expressing an answer to the question; analyzing a plurality of documents comprising natural language text, the analyzing comprising: mapping the question to one or more hypotheses, analyzing at least one passage of text in at least one of the plurality of documents to determine whether the at least one passage entails at least one of the one or more hypotheses, and in response to determining that the at least one passage entails at least one of the one or more hypotheses, identifying the at least one passage as providing supporting evidence for the answer to the question; and presenting to the user, in response to the text input, the answer and the at least one passage from the at least one of the documents identified as providing supporting evidence for the answer. 9. The at least one computer-readable storage medium of claim 8, wherein the analyzing further comprises: scoring passages in at least some of the plurality of documents based at least in part on strength of the passages' supporting evidence for the answer; and selecting one or more of the passages for presentation to the user based on the passages' scores. 10. The at least one computer-readable storage medium of claim 8, wherein generating the text output expressing the answer comprises determining the answer based at least in part on the text in the at least one passage. 11. The at least one computer-readable storage medium of claim 10, wherein determining the answer comprises selecting between at least a first answer supported by a first set of one or more passages of text in the plurality of documents and a different second answer supported by a second set of one or more passages of text in the plurality of documents. 12. The at least one computer-readable storage medium of claim 11, wherein selecting between at least the first answer and the second answer comprises comparing the first and second sets of passages based at least in part on (a) how many documents are represented in the first set of passages versus how many documents are represented in the second set of passages, and/or (b) strength of the first set of passages' supporting evidence for the first answer versus strength of the second set of passages' supporting evidence for the second answer. 13. The at least one computer-readable storage medium of claim 10, wherein determining the answer comprises: identifying a plurality of constraints posed by the question; matching different constraints of the plurality of constraints to passages in different documents of the plurality of documents; and identifying an answer supported by the passages in combination matched to the plurality of constraints of the question. 14. The at least one computer-readable storage medium of claim 13, wherein the method further comprises selecting one or more of the matched passages for presentation to the user based at least in part on how many of the plurality of constraints of the question are matched to the one or more matched passages. 15. Apparatus comprising: at least one processor; and at least one storage medium storing processor-executable instructions that, when executed by the at least one processor, perform a method comprising: receiving, from a user, a text input expressing a question in natural language; generating, in response to the question, a text output expressing an answer to the question; analyzing a plurality of documents comprising natural language text, the analyzing comprising: mapping the question to one or more hypotheses, analyzing at least one passage of text in at least one of the plurality of documents to determine whether the at least one passage entails at least one of the one or more hypotheses, and in response to determining that the at least one passage entails at least one of the one or more hypotheses, identifying the at least one passage as providing supporting evidence for the answer to the question; and presenting to the user, in response to the text input, the answer and the at least one passage from the at least one of the documents identified as providing supporting evidence for the answer. 16. The apparatus of claim 15, wherein the analyzing further comprises: scoring passages in at least some of the plurality of documents based at least in part on strength of the passages' supporting evidence for the answer; and selecting one or more of the passages for presentation to the user based on the passages' scores. 17. The apparatus of claim 15, wherein generating the text output expressing the answer comprises determining the answer based at least in part on the text in the at least one passage. 18. The apparatus of claim 17, wherein determining the answer comprises selecting between at least a first answer supported by a first set of one or more passages of text in the plurality of documents and a different second answer supported by a second set of one or more passages of text in the plurality of documents. 19. The apparatus of claim 18, wherein selecting between at least the first answer and the second answer comprises comparing the first and second sets of passages based at least in part on (a) how many documents are represented in the first set of passages versus how many documents are represented in the second set of passages, and/or (b) strength of the first set of passages' supporting evidence for the first answer versus strength of the second set of passages' supporting evidence for the second answer. 20. The apparatus of claim 17, wherein determining the answer comprises: identifying a plurality of constraints posed by the question; matching different constraints of the plurality of constraints to passages in different documents of the plurality of documents; and identifying an answer supported by the passages in combination matched to the plurality of constraints of the question.