When building software a software engineer or other system design expert creates a shared mental model of the problem space. Boxes and stick-figures or intricate flow diagrams detailing the space to be explored find their way into documentation. Descriptions made for implementation people to work out finer details.
What if the documentation was the software?
In theory the process of creating software is all design. Design progresses from large sketches to finer and finer detail. The finest of details yielding code that is finally compiled into machine language. Each refinement is fueled by human effort. Each finer detail of documentation yielding an artifact that exists merely to be consumed by the next stage in the chain.
Model Driven Architecture is an attempt to skip many of these steps and skip as closely as possible to the code that is ready to be transformed. UML diagrams drive a series of transformation engines to "compile" drawings into code. The resultant code may or may not be ready for use but it is a many great steps down the chain to complete. All of this hinging on the pretext that the programmer builds a mental model that is then transformed into code.