" The Java-Medical Diagnostics (j-MD) expert system shell is the successor to Pro-MD developed by Trendelenburg and Pohl (1988). Since j-MD may be widely used by the medical community, Trendelenburg sought an industrial partner. Sysmex (Europe), through its subsidiary Sysmex Molis which specializes in laboratory information systems agreed to support and integrate j-MD into its development strategy. The main problems were maintainability of the knowledge base, integration into modern networks, and improvement of end user acceptance. The keys to maintainable software products are i) structuring the code, ii) building hierarchies, iii) re-use of the code, and iv) versioning of software segments. All facts (or input values) are converted through decision algorithms into 'medical concepts', possessing clear meaning for any medically trained individual (basics knowledge base). One such concept may then be used directly as input to the next higher level of the knowledge base, thus creating hierarchies where the real expertise in an independent second-level knowledge base is added. The total knowledge base therefore becomes more compact and specific and thus easier to maintain. The j-MD system is provided on a modern network infrastructure. It possesses an XML interface, and the possibility to query j-MD both through the LIS (integrated solution) or through a web browser exists. Since the end user of the j-MD system is usually a clinician, an explanation subsystem is very necessary and is provided through the extensible mark-up language (XML) interface. "