MDA

• The OMG's aim with MDA is to allow businesses developing bespoke applications to concentrate on determining their business requirements for the application, but not be concerned with what particular technology platform will realize those requirements. In other words, the application is specified and implemented in a platform-independent fashion. The OMG's claim is that systems built this way should have a much longer lifespan than any given technology platform; 20 years is suggested by the OMG as typical.
• The centerpiece of MDA is the Platform Independent Model (PIM), modelled in UML.
• While the PIM is independent of technology, the platform specific model (PSM) is where the "rubber hits the road". Vendors are expected to use mapping and transformations to convert any given PIM into a PSM or indeed PSMs. MDA does not prescribe how this should be performed, but indicates that typically the transformation will be model to model, or meta-model to meta-model. In concrete terms, many vendors use tags or other metadata to annotate the PIM such that the different PSMs may be generated.
• The OMG vision also has its Meta Object Facility (MOF) playing a central part in MDA. Because the PIM and PSM are expected to be written in UML, itself a MOF language, it should be possible to define transformations written in a MOF language. Currently OMG is working on the QVT (Query, Views, Transformations) specification to support this idea. In other words, QVT allows the transformations performed by vendors between PIM, PSM and code to be standardized.
• Elaborationist MDA, is very much in keeping with how OMG's normally describe viewpoint. There are separate PIMs, PSMs and code, and the PSM is usually annotated in some fashion. Here the claim is for 50-80% code generation, with behaviour typically specified in a 3GL language.
  Translationist MDA, says that the complete system must be specified entirely within the PIM. This approach is also sometimes called Executable UML and builds on Shlaer- Mellor's work. From the PIM both the PSM and code are 100% generated completely. Indeed in practice the PSM can be substantially ignored. Behaviour is specified using an action semantic language compliant with Precise Action Semantics.