I have an app with my own - user defined class and I also use Qt framework libraries to initiate objects of other classes that are built-in. So in my class let's call it 'myclass' I create instances of Qt built-in classes and work on them. THIS IS DONE ... Now, I need to create class diagram for that. I was wondering to which out of Association, Aggregation, Composition or Generalization this could this be classified as ?
Thanks
It is not generalization as you are not inheriting in here, so it cannot qualify as an "is-a" relationship.
As for association, composition or aggregation... here you can find a pretty good explanation which is which. It is not possible to tell the right one for you without knowing your use case better. However, reading the other link will help you to understand the differences and judge based on your scenario.
Difference between association, aggregation and composition
Hope that helps.
The important thing to keep in mind about UML is that there's often no actual right or wrong answer when deciding on what to use, but some tools are better than others. UML is simply a tool for communication and as long as the tool is used in a way that everyone understands what is being communicated, then it serves its purpose.
For a class diagram, at its most basic level, you could actually model everything with just Association and Generalisation, but then this would lack detail that others may want to see.
Generalisation has a one to one relationship with inheritance, so it's clear when to use that.
Association describes any class with a relationship or dependancy with another class; quite a generalisation there(!) which is why it could be used in replacement of Aggregation and Composition.
Aggregation is used when an object (B) makes up another object (A) and B can be shared amongst other objects. For example, a library consists of books, so a book could be modelled as an aggregate of the library because other classes, could also aggregate a book, such as the person borrowing it.
Use composition when an object (B) is used directly to make up an object (A). In this case, if you were modelling the human body and had classes of organs, you would model a heart class as a composition object of a body class.
The fact that you're using the Qt framework is irrelevant to what you use to model your classes and a diagram doesn't need to model everything, just what is necessary to communicate concepts to others.
If, for example you're using container classes such as QList and QMap, you probably don't even want those in the diagram, but if you were to use QTcpSocket and inherit from it, then it may be better to show that.
Just remember, it's all about what you're trying to communicate.
