OpenID is an open, decentralized, free framework for user-centric digital identity.
OpenID starts with the concept that anyone can identify themselves on the Internet the same way websites do-with a URI (also called a URL or web address). Since URIs are at the very core of Web architecture, they provide a solid foundation for user-centric identity.
M. Sahami, S. Dumais, D. Heckerman, и E. Horvitz. Learning for Text Categorization: Papers from the 1998 Workshop, Madison, Wisconsin, AAAI Technical Report WS-98-05, (1998)