Polymorphism can be described as:

Question

I have some question for the pre-exam in the Analyst and Design information System, but I very struggle with them.

Here they are, with my answer in italic:

Asychronous message in sequence diagram can: a. All of them are correct b. Create a new object c. Create a new thread d. All of them are incorrect

Which of the following models can clearly describe dynamic concepts but cannot describe objects: a. Petri-net model b. Mixture model c. Data flow model (DFD). d. Rotation model

Polymorphism can be described as: a. Association classes with constraints b. Hide multiple different settings based on the same interface. c. Generalization of the subclasses d. Different properties and methods of subclasses have the same parent class.

Can somebody help me, confirming my answers? thanks a lot

Answer 1

Let's play it by the book, because all these questions are very tricky:

1. Asynchronous messages are in the UML specifications a distinct kind of messages and creation of an object is another kind of message. Moreover a thread in a sequence diagram is either represented as an active object or a combined fragment, none of which are created by an asynchronous message. The answer must be d: all incorrect (except d itself).

2. Dynamic concepts can be expressed in petri nets, and petri nets do not allow to express anything else than behavior. Dynamic concepts can also be expressed by a data flow diagram. However, formally the dataflow also decribes data that is exchanged, which can be viewed as a simple object without behavior, So the answer must be a. In UML one would probably use activity diagrams instead of petri nets.

3. Polymorphism: while b to d relate somehow to inheritance and interfaces, polymorphism is to use one interface that hides the many posible classes that implement it. This allows to deal with object of different classes in the exact same way, using their common interface. So the answer must be b. The answer c and d are wrong because because they could allow non-polymorphic designs with classes sharing very little in common and without possibly to deal with them in an homogeneous way.