Sourcecode is a model

If you make To-The-Scale, albeit, smaller one, "copy" of a building, you will call it a model of building, won't you? In the same sense, source code is also model of executable software. Compiler takes information from source code and converts it to executable software.

UML can model your source code, then. So, if we see in details here is ordered set of "Models". Ordering criteria is amount of abstraction.

UML - Source Code - Binary - Running Software

as you look at this,
1. UML can be used to model any of source code, Binary, running software.
2. Psuedo source code can be used to model Binary
3. Transformation from UML to running software involves CASE tools, UML tools, Compiler, Platform specific tools, Libraries and Software Mechanisms, OS, OS tools.
4. To me, highest difference of abstraction between adjacent things is between Binary and Running software. UML to source code is almost one to one. Source code to Binary is one to many. Binary to Running sofware involves time dimension.
5. To solve Software engineering problems, we need some thing between Binary and Running software - Jave and .Net has tried this by providing runtimes.