One of the difficulties associated with the use of discontinuous trial function methods is the tendency to obtain overdetermined interface conditions. A principle of information flow is set forth to guide the specification of interface conditions. The principle is based on dealing with variables that transmit information separately in each direction at an interface and on weighting a discontinuity at an interface according to the importance of the information in the region to which it is being transmitted. The asymmetric discontinuity treatment of initial-value problems follows from the principle. Treatment of boundary-value problems is illustrated by a partial-current formulation of diffusion theory. The proper number of interface conditions is obtained even for the case of different numbers of trial functions in different spatial regions.