Abstract: An expert system, such as could be used for service of a complicated physical device such as a printer or copier, exploits a knowledge base which is written in a markup language format such as SGML. The knowledge base comprises text which, if desired, can be printed out on paper to yield a traditional service manual. In addition to the typical formatting markup language tags surrounding the text of the knowledge base, hierarchical tags are provided in the electronic version of the knowledge base, to define a set of decision trees which can be accessed and navigated by an expert system. A diagnostic advisor can access specific elements of the knowledge base as needed to synthesize optimized diagnosis and repair procedures depending on an entry given by a tech rep servicing a machine. This arrangement thus supports both a printed service manual and a viewer that provides expert diagnostic advice.