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
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
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 citation15).
15Cantor, Thoughts on Functional Decomposition, The Rational Edge, April 2003, http://www.ibm.com/developerworks/rational/library/content/RationalEdge/apr03/Functiona lDecomposition_TheRationalEdge_Apr2003.pdf
12Model Driven Systems Development with Rational Products
