---
id: dwd_5k2ibrbv
type: term
slug: semantic-layer
title: "Semantic layer"
summary: "A shared definition of business metrics and dimensions, so every tool and AI agent calculates them the same way."
status: draft
classification: public
authors:
  - name: Shan Umasankar
    url: https://dealwithdata.com
    role: author
assisted_by: [Claude]
scales: [personal, business, enterprise]
synonyms: ["metrics layer"]
related: [dwd_5hhpphgh]
created: 2026-10-07
updated: 2026-10-07
version: 1
---
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*.