Comparison
Metric definitionvsSemantic layer
Metric definition
two dashboards show different revenue because one includes refunds and neither of them says so anywhere.
The precise, written statement of how a business measure is computed, including what is excluded. Most metric disagreements are not disputes about a number but discoveries that two people were computing different things, and the definition is what makes that discoverable in seconds. It has to live where it is executed rather than in a wiki, otherwise the wiki becomes the aspirational version.
Full entry →Semantic layer
the definition of active user lives in one place that every dashboard, notebook and export queries through, instead of being re-implemented in each.
A layer where metrics, dimensions and joins are defined once and consumed by every downstream tool. It exists because the alternative is the same business logic copied into a BI tool, three notebooks and a spreadsheet, drifting independently. The trade is another abstraction between the analyst and the SQL, and its success depends entirely on whether it covers enough that people stop going around it.
Full entry →