1. A computer-implemented method for building a search index: while building the search index and using the search index to respond to one or more search requests, maintaining an anchor information store, wherein each entry of the anchor information store identifies a referring document, a target document, and anchor text associated with a link from the referring document to the target document; receiving a document for processing; locating one or more entries in the anchor information store for which the document to be processed is identified as the target document; retrieving anchor text from each of the identified entries; and storing the retrieved anchor text in an entry of the search index for the document.