Application of Ilities for Ontology-based Systems Engineering

The application of ilities for the ontology-based systems engineering is investigated. Ontologies may
be used to improve the systems engineering body of knowledge. The benefits of using ontologies are
that they enable the knowledge management in terms of fundamental concepts and relationships.
Among representatives in systems engineering knowledge management, the concept of ilities became
most critical since ilities capture one of the cores of what systems engineering is all about. This work
develops the details of how ilities play the important function in the ontology of systems engineering
and show this with examples. Prior work on ilities has emphasized or restricted their application to
system level, non-functional properties. The premise of this work is that ilities can be applied with
benefit, and in some cases out of necessity, to lower levels of systems as well. The veracity of this
premise is established by providing examples that demonstrate how some ilities are passed and used
as a non-functional property of electrical and structural subsystems in aircraft. It is further
demonstrated that flowing ilities down to the subsystem or lower levels is not only a useful practice for
systems engineers, it can also be an essential step to ensure that customer needs are actually met by
the system under design or service. Systems engineers often lack the detailed knowledge of the
subsystems or components required to translate ilities into functional requirements. Thus, the system
ilities are passed down and translated from non-functional to functional requirements by subject
matter experts. We first discuss the definition, characteristics and scope of ilities within the context of
ontology. Then, we formulate the application of ilities at a subsystem level. Next, we show aircraft
engineering examples for ilities applications. The application process is formalized with diagrams, and
ilities’ relation to ontological system architecture engineering is discussed. The work concludes with a
summary and suggestions for future work.