Integrating Different Grain Levels in a Medical Data Warehouse Federation

Healthcare organizations practicing evidence-based medicine strive to unite their data resources in order to achieve a wider knowledge base for sophisticated research and matured decision support service. The central point of such an integrated system is a data warehouse, to which all participants have access. In order to insure a better protection of highly sensitive healthcare data, the warehouse is not created physically, but as a federated system. The paper describes the conceptual design of a health insurance data warehouse federation (HEWAF) aimed at supporting evidence-based medicine. We address a major domain-specific conceptual design issue: the integration of low-grained, time-segmented data into the traditional warehouse, whose basic grain level is higher than that of the time-segmented data. The conceptual model is based on a widely accepted international healthcare standard. We use ontologies of the data warehouse domain, as well as of the healthcare and pharmacy domains, to provide schema matching between the federation and the component warehouses.