Big corporate rivalries - Coca-Cola and Pepsi, Boeing and Airbus, McDonald's and Burger King - tend to have one thing in common: competition for the same business.
That's why Facebook and Apple's feud is so intriguing.
They're both big technology companies, and that's where the similarities end.
Almost all of Facebook's revenue is from advertising but it provides only a small fraction of Apple's, which comes mostly from devices and its App Store.
