This paper reports on the development of a realistic knowledge-based a
pplication using the MOBAL system. Some problems and requirements resu
lting from industrial-caliber tasks are formulated. A step-by-step acc
ount of the construction of a knowledge base for such a task demonstra
tes how the interleaved use of several learning algorithms in concert
with an inference engine and a graphical interface can fulfill those r
equirements. Design, analysis, revision, refinement and extension of a
working model are combined in one incremental process. This illustrat
es the balanced cooperative modelling approach. The case study is take
n from the telecommunications domain and more precisely deals with sec
urity management in telecommunications networks. MOBAL would be used a
s part of a security management tool for acquiring, validating and ref
ining a security policy. The modeling approach is compared with other
approaches, such as KADS and stand-alone machine learning.