Architecture :: Inherited DTOs, How To Implement The Layers Facade, Bll And Dal?

I doubt how to implement the layers
FACADE, BLL and DAL, using
DTOs specialized ..
where:

public class ClassA
{
private int _Test1;
public int Test1
{
get { return _Test1; }
set { _Test1 = value; }
}
}
public class ClassAB : ClassA
{
private int _Test2;
public int Test2
{
get { return _Test2; }
set { _Test2 = value; }
}
}
public class ClassAC : ClassA
{
private int _Test3;
public int Test3
{
get { return _Test3; }
set { _Test3 = value; }
}
}

In the database, there is the 3 tables, as described above.how do I implement the facade, bll and dal? only one class for 3 DTOs?