Many UML modeling tools like Visual Paradigm allow you to generate code based on your models. One big problem in this approach is that it is hard to make change

Many UML modeling tools like Visual Paradigm allow you to generate code based on your models. One big problem in this approach is that it is hard to make changes beyond that. Some people want to customize the generated code, but that means that if you want to make changes to the diagram you somehow have to merge back the changes which were manually made. If you are interested in this you should check out a company called Mendix, which is building a SaaS platform for building applications using graphical tools, and the Eclipse Modelling Framework, which is a huge project aiming to add modelling and code generation capabilities to Eclipse (in my experience it is slightly academic, in the sense that you often encounter bugs or cryptic errors in practical use).