Each document of a corpus is identified by its persistent and unique Uniform Resource Identifier (URI), also known as its Document URI.
While indexing a document in a PaF, a reply URI must be provided. This URI is used to redirect the user to the correct page when selecting a reply. Reply URIs are usually tightly integrated into the application hosting the search engine. They are usually different from documents URIs in the PaF, except for crawled documents. See URI.