Please I need help in understanding this two approaches in the uml world. I am a programmer who is new to uml. I just started learning uml lately but kept getting this phrase asked all the time. - Are you modelling or drawing?. An explanation is needed with clear examples. This link hinted just a little but I am stil confused -- http://modeling-languages.com/drawing-tools-vs-modeling-tools/
UML is a modeling language, which has a graphical notation. Its semantic is precisely specified by UML 2.5 standard of the OMG and also the international standards ISO 19505-1:2012 and 19505-2:2012 (although the latter corresponds to UML 2.4.1).
THere are two different approaches to UML diagramming. And it's heavily influenced by the tools you use:
Drawing tools generally offer UML shapes to be used in drawings. But there is no deeper meaning behind the shapes. It's only pictures. These tools would allow you to mix a use case with a class or an actor in a deployment diagram. The advantage is that you can do what you want. The inconvenience is that what you want may not be compliant.
Real modeling tools let you combine only valid UML elements together and ensure consistency of what you draw with the deeper meaning of the UML language. And they build a true and comprehensive model behind the scene by combining all the facets of the different diagrams.
Modeling tools can do smarter things. They can relate for example a class to their object instantiations in sequence diagram. They can help you to find all the other models in which a specific class is used. If you rename a class or add a property in one diagram, it'll be automatically reflected in all the others.
Modeling requires more discipline, but it's more powerful in the end. Some modelling tools can even use their understanding of UML to generate code out of the model.