15. A computing device with a processor and memory for training a document ranking component, comprising: a component that provides representations of documents along with a labeling of some of the documents, the labeling for a document indicating relevance of that document to a query; a component that determines the similarity between pairs of documents represented based on analysis of content of each pair of documents; a component that propagates the relevance of labels of the labeled documents to the unlabeled documents based on the determined similarity between documents such that the propagation of the relevance of a label document to an unlabeled document increases with increasing similarity between the labeled document and the unlabeled document; and a component that generates a document ranking component to rank relevance of documents to a query based on the propagated relevance of the documents so that, after the document ranking component is generated, the document ranking component is adapted to rank documents of search results of a query.
15. A computing device with a processor and memory for training a document ranking component, comprising: a component that provides representations of documents along with a labeling of some of the documents, the labeling for a document indicating relevance of that document to a query; a component that determines the similarity between pairs of documents represented based on analysis of content of each pair of documents; a component that propagates the relevance of labels of the labeled documents to the unlabeled documents based on the determined similarity between documents such that the propagation of the relevance of a label document to an unlabeled document increases with increasing similarity between the labeled document and the unlabeled document; and a component that generates a document ranking component to rank relevance of documents to a query based on the propagated relevance of the documents so that, after the document ranking component is generated, the document ranking component is adapted to rank documents of search results of a query. 16. The computing device of claim 15 wherein the document ranking component implements a regression based ranking algorithm.