A data warehouse: the questions we get asked most

The advice here is unglamorous, which is probably why it gets skipped. The questions about a data warehouse that come up most often on our calls.

Most data problems are ownership problems that turned into technical ones. If it only works because one person remembers to do something, it does not work yet.

Do we need to care about this?

Reporting queries and application queries want different shapes. Where this goes wrong is almost never a lack of knowledge. It is the sort of thing that looks like polish right up until it costs you an enquiry.

Can it wait until after launch?

Occasionally. More often the post-launch version costs several times the pre-launch one. Small and consistent beats large and occasional here.

How do we know it is working?

Start with the questions, not with the schema. Small and consistent beats large and occasional here. Check it against what you would want a competitor's site to get wrong.

How to tell if yours is fine

Numbers get quoted in meetings long after anyone remembers how they were calculated. Three things worth confirming about a data warehouse before you move on:

• Someone can say what the current setup is without going to look
• Separating them stops reports taking the product down — 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.