private void CreateAggregation()
{
TypeShape shape1 = first as TypeShape;
TypeShape shape2 = second as TypeShape;
if (shape1 != null && shape2 != null)
{
diagram.AddAggregation(shape1.TypeBase, shape2.TypeBase);
}
else
{
MessageBox.Show(Strings.ErrorCannotCreateRelationship);
}
}