THE ORIGIN OF (DOCUMENT) SPECIES

The World Wide Web's extraordinary reach is based in part on its open assimilation of document formats. Although Web transfer protocols and addressing can accommodate any kinds of resources, the unique applicat ion context of a truly global hypermedia system favours the adoption o f certain Web-adapted formats. In this paper we consider the evolution ary record that has led to the ascent of the eXtensible Markup Languag e (XML). We present a taxonomy of document species in the Web accordin g to their syntax, style, structure, and semantics. We observe the pre ferential adoption of SGML, CSS, HTML, and XML, respectively, which le verage a parsimonious evolutionary strategy favouring declarative enco dings over Turing-complete languages; separable styles over inline for matting; declarative markup over presentational markup; and well-defin ed semantics over operational behavior. The paper concludes with an ev olutionary walkthrough of citation formats. Ultimately, combined with the self-referential power of the Web to document itself, we believe X ML can catalyze a critical shift of the Web from a global information space into a universal knowledge network. (C) 1998 Published by Elsevi er Science B.V. All rights reserved.