http://doi.acm.org/10.1145/122974.123011 Mark Bernstein Peter J. Brown Mark E. Frisse Robert J. Glushko George P. Landow Polle Zellweger Structure, Navigation, and Hypertext: The Status of the Navigation Problem. 363-366 HT1991/P363.pdf 1991 conf/ht/91 Hypertext db/conf/ht/ht91.html#BernsteinBFGLZ91