As part of my PhD project, I have been developing a prototype case-based reasoning system (KICS) which can assist domain experts in the relaxation process of building regulations (see papaers 1, 2 and 3). The system helps the experts to interpret and make decision in appeal cases by providing the experts with relevant legal rules and cases. In traditional legal decision support systems, it has been regarded as natural to represent legal rules in statutes in terms of decision rules and to link these rules to a separate case-based reasoning system for handling cases. However, we take a view that legal rules in the statutory regulations are the results of accumulation and generalisation of the rulings made in case histories and have introduced a unified case-based model of legal rules from both the statutory regulations and case histories. The system uses this model to construct the model knowledge base of legal rules, which serves both as a framework for the interpretation of legal rules and as indexes to cases stored in the case library. The system retrieves relevant information using the notion of implied similarity as well as structual mapping. Relevant legal rules and cases including argumentation surrounding cases are explained to the user and the user makes decisions about relaxation. Only relaxed cases are integrated into the model knowledge base. The prototype system is being implemented in Prolog and will be evaluated with 23 appeal cases from the Building Directorate of the Scottish Office.