9. A computer system for ranking documents, comprising: a memory storing computer-executable instructions of: a sentence classifier; a document rank classifier trained based on classifications of sentences of documents, the classifications being generated using the sentence classifier, and trained based on ranks of documents; and a component that classifies sentences of a document using the sentence classifier, represents the document by classifications of its sentences as determined by the sentence classifier, and applies the document rank classifier to the classified sentences to generate a rank for the document; and a processor that executes the computer-executable instructions stored in the memory.
9. A computer system for ranking documents, comprising: a memory storing computer-executable instructions of: a sentence classifier; a document rank classifier trained based on classifications of sentences of documents, the classifications being generated using the sentence classifier, and trained based on ranks of documents; and a component that classifies sentences of a document using the sentence classifier, represents the document by classifications of its sentences as determined by the sentence classifier, and applies the document rank classifier to the classified sentences to generate a rank for the document; and a processor that executes the computer-executable instructions stored in the memory. 14. The computer system of claim 9 wherein the classifiers are trained using an Ada-boosting algorithm.