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User Driven Design

Gautier DI FOLCO November 08, 2022 [Software engineering] #software engineering #product #design

Last week I was watching Mauro Servienti - All Our Aggregates Are Wrong.

At some point he stated that users tend to think in terms of data.

I had a female friend, a long time ago, which was studying to be part of private clinics/public hospitals management team. Let me emphasize this, her future position would include: people management, hiring, fundraising, budget management.

Despite that, she had some lessons on "computer science", I had a look at some of her homework, none of them were making sense. Basically, on of them was a kind of database table modeling (mostly boxes with a name, attributes, and links between them).

Once the initial shock passed:

To illustrate that, let's say you discuss with someone in charge of an e-commerce website, (s)he might describe a basket with:

So, you'll be tempted to model it as:

data Basket = Basket
  { items :: [Item]
  , discounts :: [Discount]
  , totalPrice :: Price
  , shippingAddress :: Maybe Address
  , carrier :: Maybe Carrier
  , status :: Status

Great, you have just let the stakeholder strap you in his/her design.

Just to be sure we are on the same page: when you go to the surgeon, would you request him/her what you want (i.e. fix your broken arm), or how you want it (i.e. the complete operating protocol).

Note: IMO, focusing on the how denotes a lack of trust

Whenever I tackle a subject, I start with the actions, let's grab our stakeholder again, a customer will:

To give a hint on what goes wrong, the carrier does not care about the discounts. Everything is coupled around Basket which is also an issue since we cannot express that a shipping address have been set before going in the shipping part.

That's when I leverage DDD's Bounded Contexts.

I can then come up with:

computePackage :: [Items] -> Package -- size, weight, insured price
carriersProposal :: Package -> Address -> m [CarrierProposal] -- Name, Price, Delay/Proposed delivery options
bill :: [Item] -> [ExtraDiscount] -> CarrierProposal -> Bill
pay :: Bill -> m ()

Then, and only then, I can work on my types structure, without being restrained by my stakeholder design.

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