In the UML diagram given, we see two classes,ClassAandClassB, withClassBinheriting fromClassA.ClassA has two attributes,positionof typeIntegeranddescriptionof typeString.ClassBintroduces an additional attribute,versionof typeReal.
Looking at the instance specifications (the right part of the diagram), we have three instances:a1of typeClassA
,b1of typeClassB, andb2also of typeClassB.
In UML, an instance specification must comply with the structure of its classifier, which means an instance of ClassAmust show slots for bothpositionanddescription, whereas an instance ofClassBmust show slots for position,description, andversion.
In the provided diagram, instancea1ofClassAonly shows a slot forposition. This is an error because it does not show a slot fordescription, which is a defined attribute ofClassA. To correct this error, we would need to add adescriptionslot toa1.
This means that the correct answer is:
B: Add a description slot to a1.
The other options do not correct the error in the model:
A) Specifying unique values forpositiondoes not address the missingdescriptionslot ina1. C) Changing the type ofClassB.versionfromRealtoIntegeris not required by any UML constraint in the context given. D) Changing the type ofClassA.positionfromIntegertoRealdoes not address the missingdescriptionslot ina1and is unrelated to the inheritance structure.