I cant teach you anything correctly if I don't know you are really doing. Sure I get you are asking "how to implement Class Table Inheritance using Doctrine ", but from my position, I have no idea if that is actually the correct solution to your problem. By forcing me to focus on your attempt instead of the problem you are locking yourself out of any other potential or better solutions. If you just plain ol wanted to learn Class Table Inheritance using Doctrine, that is one thing, but it comes across as though you have deemed this to be the solution to a problem at hand.
I know your not asking me to build you something. I was trying to get across an easy way for me to understand what I was asking of you. The very nature of all your posts being outside the realm of what many of us with numerous years experience have ever seen makes it even more important to know what the actual project is. Honestly, I have often wondered if PHP is even the right language for whatever it is you are doing. Since I, and others have no clue to what it is, who's to say.