Tools for immunization guideline knowledge maintenance. I. Automated generation of the logic "kernel" for immunization forecasting.

IMM/Def is a prototype computer program designed to facilitate the building and maintenance of a rule-based program which performs childhood immunization forecasting. An immunization forecasting program takes as input a child's immunization history and produces recommendations as to which vaccinations are due and which should be scheduled next. A significant amount of the knowledge required for immunization forecasting can be expressed in tabular form, including the parameters that indicate the minimum age when each dose may be given and the minimum intervals between doses. The choice of which of these sets of parameters apply to a particular case depends upon additional clinical logic. To perform forecasting, this logic must be applied in three temporal contexts: (1) a dose is due now, (2) a dose is not yet due, and (3) a dose must be scheduled to follow a dose which is due now. Building and maintaining this logic by hand is a formidable challenge. IMM/Def demonstrates how this task can be simplified by first defining immunization "definition logic" which can be automatically translated into if-then rules for each of the three contexts. The approach has been applied successfully to the six childhood vaccination series which are routinely administered. A key advantage is that IMM/Def allows one to have two specifications of the logic that can be examined independently and that can be cross-checked to help assure completeness, consistency, and accuracy of the logic. The paper describes how IMM/Def performs its translation and discusses several design issues and lessons learned.