None has yet been implemented as an open system with true links and filtering. This work will shape both the nature of hypertext publications and the software used to manipulate and display them. A goal for design of a database level is to enable use of the full range of higher-level facilities and idioms that have evolved in the current generation of private hypertext systems. This will enable us to use knowledge we have already evolved. Perhaps not very well, yet an attempt may be worth the effort.
Several approaches seem reasonable.
One is to reason by means of analogies to present paper media, seeking analogous problems and solutions. Another is to place advantages and problems within the analytical framework of expression, transmission, and evaluation, relating them to critical discussion and the evolution of knowledge. Expression Hypertext publishing will aid expression in several ways. These advantages in cost and quality of expression seem great. Hypertext won't be a powerful medium of expression if no one writes for it.