Computerized guidelines have been utilized for several decades by now. Systems based on computerized-guidelines often intertwine (1) medical knowledge representation, (2) guideline procedures and (3) hospital workflows. This induces several drawbacks. Most prominent problems include non-shareability of the computerized guideline between hospitals, limited accessibility of the computerized guideline for humans, and an unclear, often confusing combination of hospital-specific workflow and guideline-induced control flows. This article proposes a 3-layer modelling approach strictly distinguishing the aforementioned three aspects to overcome the respective problems. We applied the 3-layer approach to the implementation of a guideline-interpreting software module in the context of the Medical Informatics Initiative Germany (here: SMITH Project) and comment on the resulting implications for the software design of that module.