Enabling a domain expert to maintain his own knowledge in a Knowledge Based System has long been an ideal for the Knowledge Engineering community. In this paper we report on our experience with trying to achieve this ideal in a practical setting, by building a maintenance tool for an existing KBS. After a brief survey of various approaches to this problem described in literature, we select a domain- and task-specific modelling approach as the most promising and appropriate. First, we construct a domain ontology and a task model for the KBS system to be maintained, as well as a task analysis of the maintenance tool itself. The maintenance tool is subsequently implemented using a two layer architecture which seperates domain and system concepts. Although no full-scale evaluation has been undertaken, we report on our initial experience with this approach and present our conclusions. 1 Motivation In Software Engineering it is well-known that the majority of the costs for software projects ...