Guidelines For URI Naming Policies - advice on policies for URI naming that are sensitive to persistence issues, Ariadne, March-April 2002, Brian Kelly
Uniform Resource Identifiers (URI): Generic Syntax - (IETF RFC 2396, Updates RFC 1808 and RFC 1738) defines the generic syntax of URI, including both absolute and relative forms, and guidelines for their use, Tim Berners-Lee, R. Fielding, L. Masinter, August 1998
URIs, URLs, and URNs: Clarifications and Recommendations 1.0 - (Report from the joint W3C/IETF URI Planning Interest Group, and W3C Note as of 2001-10-22) outlines the difference between classical and contemporary URI partitioning; explains the relationship between URIs, URLs, and URNs; describes how URI schemes and URN namespace ids are registered; and sets forth recommendations