Originally Posted by
dougzz
Thank you, but why couldn't the fare be constructed using the prime flight number, and applying whatever revenue rules in the situation of connecting flights. I suppose the answer is code shares are just the way airlines have chosen to do this. I guess the answer is that was the chosen method. I manage an ageing OpenVMS system, and get quite irritated when someone says "but why was it done this way" when the question refers to something done 20+ years ago, and is just a small part of a larger process.
The underlying construction of fares is nearer 60 years old. But the key reason is if you buy ticket from A to B it will have a fare basis with a set of rules. This set of rules will say which other sectors can be added, which flight numbers, minimum stay locations, which zones the tickets can be sold in, which end-on constructions are allowed. If it's a BA ticket, the rules won't have a long list of AA flights but will say it's ok to add in BA0nnn to BA9nnn. There's often a view out there that you can somehow add all tickets together into one booking, maybe even add a redemption ticket too, but just not how it was designed and simply won't be physically issued. There are also some anti-trust and other regulatory restrictions in this field.