Building up a knowledge base is a complex task in which theoretical kn
owledge needs to be integrated with practical experience. This integra
tion can be supported by a system that can manage linking between rule
s, representing experts or textbook or theoretical knowledge and facts
(or data), representing cases from practice. Conflicts between rules
and real-world cases can have diverse causes. Case data can be noisy o
r inconsistent or both. We use rules to filter cases and confine noise
or inconsistency. However, rules can be overly general and can classi
fy more cases than intended. Then machine learning can be used to find
additional restrictions for the rules. If, however, no significant si
milarities can be determined between the misclassified cases, we seek
additional expert input to support effective implementation of learnin
g tools. Using a case subset, we capture expert input and formulate a
set of ''enriched'' cases. We then use the enriched cases to learn add
itional rules and to introduce practical features to validate and refi
ne the original rule base. In this paper, we discuss the role of machi
ne learning as a vehicle for supporting rule and data validation. We d
emonstrate our results by an application of the MOBAL system to a real
-world medical domain.