Cakes and Systems Definition

In systems Engineering thinking, and more specifically in railway signalling I guess, the term system definition means defining what your product (or system) is going to do. It sets up the case so that when later the product is going through safety case analysis, it is clear what is covered by the design and what is not. It creates a boundary between the product, which is the responsibility of the supplier, and the outside world, which is not under the supplier domain of control.

So system definition is important. If the above is unclear, let me present an analogy. Let’s say a friend is organising a birthday party, and asks you to bring a cake.

“What kind of cake?” you would ask.

Any cake, came the reply. But then if you bring a pancake, it would most likely not fulfil the criteria.

“But you said any cake!”

“Okay next time bring a normal cake,” said the friend.

What is a normal cake? You then bring a vanilla cake.

“I don’t really like this cake. It’s too plain.”

“But you said a normal cake. This is the most normal cake I can find.”

“Yeah normal doesn’t mean plain. I was thinking like a chocolate cake or something,” said the friend.

So next time you brought a chocolate cake for the friend’s birthday party.

“Nice. Where is the candle?” asked the friend.

“What candle?”

“It’s a birthday cake. It needs to have candles. At least one.”

“You said to bring a cake! You didn’t say anything about candles!”

And the dialogue continues on and on.This doesn’t even include cases where there is food allergy, dietary preferences etc. So you see, even in something as simple as a cake, can there be lotsa misunderstandings that can happen. You need to define the cake.

Similarly this goes back to the first paragraph, and just analogously describes how things can go wrong when the systems definition is not done properly. But yeah, it happens.

At least with a cake, you can eat it. But a botched product is likely going to have further consequences than that.

Thanks for reading.