A short guide to data modelling

We end up explaining this on discovery calls often enough that it deserved writing down. Everything we would tell a client about data modelling in the time it takes to drink a coffee.

Numbers get quoted in meetings long after anyone remembers how they were calculated. It rarely shows up as a line item, which is exactly why it slips.

What it costs to ignore

The model outlives the application built on top of it. There is a version of this that is over-engineered, and it is worth avoiding. It rarely shows up as a line item, which is exactly why it slips.

How we handle it

Name things the way the business names them. The teams that handle this well are rarely the ones with the biggest budgets. It is the sort of thing that looks like polish right up until it costs you an enquiry.

Common failure modes

Model what is true, not what is convenient this quarter. The teams that handle this well are rarely the ones with the biggest budgets. Assume whoever inherits this will have half your context and none of your patience.

The short version

Data outlives the applications built on top of it, which is why the model deserves more thought than the screens. Three things worth confirming about data modelling before you move on:

• Someone can say what the current setup is without going to look
• The model outlives the application built on top of it — and you know whether that is true here
• There is a way to tell whether the last change to this helped

Pick the one that would hurt most if it failed, and start there.