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12 Model Driven Systems Development with Rational Products
subsystems was given to an independent team for development. During the
project, each team independently discovered the need for a database with the
satellite's orbital history (the satellites can, to some extent, be steered to
different orbits as needed). So each team built its own separate database,
using separate formats. But the information needs to be consistent for the
overall system to operate correctly, and now, the effort required to maintain
these three databases is excessive and could easily have been avoided had
the team done some kind of object analysis, including a study of the
enterprise data architecture.
15
MDSD seeks to avoid this kind of duplication of functionality by promoting a
breadth-first analysis of functionality across a set of collaborating entities.
Collaboration, both in the development process, and in system functionality is at
the heart of MDSD.
Traceability
Traceability is usually a requirement for the systems that we build. Often, it is an
explicit contract item: You
shall provide traceability matrices to demonstrate how
the requirements of the system have been implemented and tested. Apart from
contract requirements, traceability is needed to do effective fault or impact
analysis: If something goes wrong, we must determine what caused the fault; if
some requirement must be changed, or added, we must determine what parts of
the system will be affected.
Providing traceability can be an onerous requirement. Many times it is done
manually at significant cost both in the original development and later through
testing and maintenance. Manual methods of providing traceability are difficult to
maintain and error-prone.
MDSD can help lighten the burden of providing and then maintaining traceability
information. Three of the core processes of MDSD, operations analysis, logical
decomposition and joint realization tables, allow for a great deal of the
traceability problem to be automated. SysML provides semantic modeling
support for traceability. The Rational Software Delivery Platform also provides
tools and support for traceability.
Well defined semantics
Talking about the various parts of a system, at their different levels, and talking
about their relationships, can be difficult and confusing without well defined
semantics. MDSD has a well defined meta model which promotes clarity of
discussion (see the aforementioned citation
15
).
15
Cantor, Thoughts on Functional Decomposition, The Rational Edge, April 2003,
http://www.ibm.com/developerworks/rational/library/content/RationalEdge/apr03/Functiona
lDecomposition_TheRationalEdge_Apr2003.pdf