First an example to discuss:
class Foo
{
// Attributes:
int attribute1, attribute2;
// Methods:
virtual void Foo1()
{ /* With or without Implementation */ }
virtual void Foo2()
{ /* Also with or without Implementation */ }
};
class ExactDuplicate: Foo // No New Attributes or Methods
{
virtual void Foo1()
{ /* A new Implementation */ }
// Also there might be new Implementations to other methods
};
class ExtraMethods: Foo // Having New Methods
{
virtual void Foo3()
{ /* Implementation */ }
};
class ExtraAttributes: Foo // Having New Attributes
{
int attribute3;
};
I had a discussion -with my teacher- about the "is A" and the "is Like A" relationships and how do they differ.
My Opinion (which I read somewhere I can't remember) is that the "is A" relationship is between a Parent Class and a Child Class which is inherited form it, and it's not affected by adding new methods or attributes, so any instance from the child class "is A" Parent class, in the above exmple, every ExactDuplicate, ExtraMethods, or ExtraAttributes "is A" Foo. While the "is Like A" relationship is between two Child classes inherited from the same Parent class, in the above exmple, every ExactDuplicate "is Like" every ExtraMethods or ExtraAttributes, and the reverse.
My Teacher's Opinion was that the "is A" relationship is between a Parent Class and only the Child classes which do not add any extra methods or attributes, so in the above example there is only one "is A" relationship between Foo and ExactDuplicate. While the "is Like A" relationship is between a Parent Class and the Child Classes which add extra methods or attributes, so in the above example, there is an "is Like A" relationship between Foo and each of ExtraMethods and ExtraAttributes.
I think that, the "is A" relationship as defined by my teacher is not really useful because in most cases there is no reason to change the implementation if nothing is added. This is a point. Another, a Car "is NOT Like a" Vehicle, it actually "is A" Vehicle, while a Van "is Like A" Car, since both associate some characteristics.
So which is correct and why?, I would highly appreciate explaining.
Also if my teacher's opinion is the true one, does adding only Attributes make the relationship an "is Like A" relationship, or it needs adding new methods to become an "is Like A" relationship? and what (if exists) is the relationship between the Child Classes.
Hope my questoin is clear and understandable.
Any Help would be Greatly Appreciated :)