Resumen
Abstract representations of content which allow it to be automatically adapted to suit the delivery context, have emerged historically with the development of markup languages intended to facilitate the storage and processing of electronic documents. This technological tradition is reviewed in the first part of the paper, focusing predominantly on the nature and advantages of a ?single authoring? approach to the creation of content. Some of the lessons to be derived from the evolution and deployment of markup systems are also discussed, then applied, in the second part of the paper, to the question of how such abstractions can be extended to the design of user interfaces. Innovative work related to the generic specification of user interfaces is reviewed. It is argued that the advantages of an abstract approach depend for their realization on the development of more expressive style languages and more sophisticated adaptation mechanisms, as well as continued refinement of the semantics of markup languages themselves.