The Pizza Ordering Interface
If I were to call up any pizza place in town, I guarantee you, this is the conversation flow I would get:
Them: “Hi, Pizza Brand Pizza. This is Julie speaking. How can I help you?”
Me: “Yes, I’d like to order delivery.”
Them: “Delivery? Sure. Can I get your phone number?”
Me: “867-5309.”
Them: “Ok, I have you at 123 Fancy Pants Lane. Is this correct?”
Me: “Yes.”
Them: “Ok, what can I get you?”
Me: “I’d like a large pizza with mushrooms, green peppers, and onions.”
Them: “Ok, large pizza with mushrooms, green peppers, and onions. Anything else?”
Me: “Yes, I’d like a large cheese pizza.”
Them: “Ok, large cheese pizza. Anything else?”
Me: “That’s it.”
Them: “Ok, you’re total is $41.34. Will that be cash or card?”
Me: “Card.”
Them: “Ok, I’m ready for the digits when you are.”
Me: “Ok. 1234 5678 9012 3456.”
Them: “Ok, expiration date?”
Me: “10/25.”
Them: “Security code?”
Me: “987.”
Them: “Ok, you’re all set. A driver will be out in about 45 minutes.”
Me: “Ok, thanks.”
Them: “You’re welcome.”
In fact, I expect that if I were to call up any pizza place in the whole country, I would get the same flow. This would probably be true in the whole world; perhaps just swap out English for some other language.
How can this be? How can all pizza restaurants follow the same script? Was there a Zoom call that representatives from all pizza establishments joined where everyone agreed that this would be the only way to order pizza? A “continental congress of pizza,” if you will?
It turns out there is a well-defined pizza ordering interface that is implemented by all pizza restaurants because all pizza restaurants need the same things.
Pizza restaurants need a phone number that customers can call, and they need to publish this phone number where customers can see it, or there will not be orders coming in.
There is a set of data points that all pizza restaurants need from customers:
- Contact Info
- Order Info
- Payment Info
And customers like to know:
- The total cost for their order
- How long will they have to wait until they get that “lovely cheese pizza, just for me”
Information needs to be exchanged in a certain order. Imagine if the customer asked for their total at the beginning of the call: “But sir, you haven’t ordered anything yet!” And I don’t think the customer would be happy if the restaurant asked for the credit card first: “How much are you charging on my card?!” Or if they established your address at the very end of the call: “Oh, I’m sorry, you appear to be outside our delivery radius; we’ll have to cancel your order.” What if they took down your phone number at the end of the call? Re-establishing call interruptions would be difficult: “Uh yeah, I was the guy that was ordering a pepperoni pizza…”
There needs to be a way to handle and prevent issues. The person taking your order needs to confirm your order to prevent mistakes. If the kitchen has a question about your order or if the delivery driver can’t find your address, they need a phone number to call. And if there are weird, exceptional situations, there needs to be a manager that can address the issues.
When designing communications between two modules in any system, the same areas need to be established:
- Why are the parties communicating?
- What data will need to be exchanged?
- In what order does the communication need to take place?
- How will communication errors or interruptions be handled?
For further reading on interfaces, including more on the pizza interface, I recommend the now out-of-print Pragmatic Programmer’s Interface Oriented Design by Ken Pugh.
There is also some good information on interface-based programming over on Stack Overflow here and here.