In this paper we propose a formal interface design methodology based on user knowledge. The general methodology consists of 1) obtaining distance estimates for pairs of system units (objects, actions, concepts), 2) transforming the distance estimates using scaling techniques (e.g., Pathfinder network analysis), and 3) organizing the system interface based on the scaling solution. Thus, the organization of the system is based on the cognitive models of users rather than the intuitions of designers. As an example, we discuss the application of our methodology to the design of a network-based indexing aid for the UNIX on-line documentation system (MAN).

Boundary points of a threshold function fare those vertices of the n-cube that produce a minimal irredundant set of inequalities for the realization of f. In this paper they are shown to be those vertices that can be contained in separating hyperplanes. With this theorem it is shown that knowledge of canonical boundary points of self-dual canonical threshold functions allows complete determination of boundary points of equivalent functions. This provides a compact and geometrically interesting characterization of threshold functions.