Semantic layer
A shared definition of business metrics and dimensions, so every tool and AI agent calculates them the same way.
Also called: metrics layer
A semantic layer defines calculations once (metrics, dimensions, joins) over physical data, and every BI tool and AI agent queries through it. The Open Semantic Interchange (OSI), now Apache Ossie, is the emerging format for exchanging these definitions between tools.
Example: Total Exposure = SUM(OUTSTANDING_BAL_AMT), synonyms "UPB", "principal".
Not to be confused with semantic discovery, a catalog activity that infers what a column means. A semantic layer defines how to calculate.