On the Expressiveness of Links in Hypertext Systems

machine that behaves as a pushdown automaton. In practical terms, Proposition 5.1 states that the history mechanism and the back button introduce a new class of hypertext systems, whose navigation space, i.e. hyperconnectivity, can only be provided by a more powerful class of hypertext systems. It should be observed that the hyperconnectivity generated by links is in fact specified by the authors when they author documents. The hyperconnectivity derived from back buttons offers new navigation capabilities to the user, but it is provided by the hypertext system itself. In the following sections, we present other mechanisms of linking that allow authors to specify the hyperconnectivity they wish.