UML Class diagram and code generation

Dear VP Support,

As far as I understand, UML defines a meaning for each element it contains: associations, composition, aggregation, inheritance, multiplicity etc. I presume every element of the diagram must be reflected in the generated source code. I started small diagrams with just a few elements (2 classes with different type of associations etc.) to see how each element was generated in source code. Instead of this, when I generate source code from a given diagram it looks as if many elements were completely ignored. I must be missing something since it shouldnt be possible to have UML elements ignored in the generated code. A rich class diagram would generate poor source code.

Thanks in advance