The motivation is to enable the common and consistent description of persons (using the existing semantics of vCard) and to encode these in RDF/XML. RDF is an application of the Extensible Markup Language XML.
F. Abel, N. Henze, E. Herder, and D. Krause. User Modeling, Adaptation, and Personalization, volume 6075 of Lecture Notes in Computer Science, Springer Berlin Heidelberg, (2010)