A rule that competes
with a shortcut loses

Most BI tools have the features needed to keep definitions consistent. The features are not the issue. The issue is that using them is optional, and optional loses over a long enough period.

The two paths problem

In a typical deployment there are two ways to get a number into a report. The correct one goes through the governed model, involves a request or at least a convention, and takes longer. The other one is a measure typed directly into the report, and takes a minute.

Both paths lead to something that looks identical on screen. Nothing marks the second one as different for the person reading it later.

Why good teams still drift

This is not a story about careless people. The drift comes from ordinary pressure: a deadline, a board pack due, somebody senior asking for a variation while standing at your desk. Every individual decision to take the short path is defensible.

The aggregate of those decisions, eighteen months in, is a reporting estate where nobody can tell which numbers are governed and which were typed.

What structure means here

Structural means the short path does not exist. Not discouraged, not flagged in review, not caught by an audit later. Unavailable, because the reporting surface has no mechanism for defining a metric locally.

That is a real constraint and it will occasionally be annoying. The trade is that a number in a report can always be traced to a definition somebody agreed to, without checking.

How to tell which one you have

Pick a report nobody senior looks at. Find a measure in it. Ask where that measure is defined. If the answer requires opening the report to find out, definitions are a practice at your organisation, not a constraint, and the drift is already underway.