The PAPI system: point of access to providers of information. - Rodrigo Castro-Rojo; Diego R. López (Comput. Networks, 2001)

Ubiquitous Internet Access Control: The PAPI System. - Diego R. López; Rodrigo Castro-Rojo (DEXA Workshops, 2002)

Attribute-based Interactions in a Distributed Authentication and Authorization Infrastructure. - Diego R. López; Rodrigo Castro-Rojo (DEXA Workshops, 2003)