OrionBelt Semantic Layer

Compile and execute YAML semantic models as analytical SQL across multiple database dialects

OrionBelt Semantic Layer is an API-first semantic engine and query planner for AI agents that compiles and executes declarative YAML model definitions as optimized SQL for BigQuery, ClickHouse, Databricks, Dremio, DuckDB/MotherDuck, MySQL, Postgres, and Snowflake. Query using business concepts — dimensions, measures, and metrics — instead of raw SQL.

Analytics as Code — Define your analytical semantics in version-controlled YAML, compile to dialect-specific SQL, and execute against live databases, all through a single API. No BI tool in the middle: the full loop from declarative model to query results is programmable, reviewable, and reproducible.

Companion Project: OrionBelt Analytics — an ontology-based MCP server that analyzes database schemas and generates RDF/OWL ontologies. Together they let AI assistants navigate your data landscape through ontologies and compile safe, dialect-aware analytical SQL.

Table of Contents

• Try it in 30 Seconds — Live Demo | Colab | PyPI | Docker
• Claude Desktop / MCP
• Why OrionBelt?
• Features
• Example
• Gradio UI
• Documentation
• Status & Roadmap
• Companion Project
• Development

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Try it in 30 Seconds

Option A: Live Demo (no install)

Open the Live Demo — Gradio UI with a pre-loaded example model. Paste a query, pick a dialect, see SQL instantly.

API explorer: Swagger UI | ReDoc

Option B: Google Colab (no install)

— Interactive notebook with TPC-H data: explore the model, compile queries across dialects, execute against DuckDB, and see results. Requires Python 3.12 runtime.

Option C: Install from PyPI

pip install orionbelt-semantic-layer

Then paste into a Python REPL:

from orionbelt.parser import ReferenceResolver, TrackedLoader
from orionbelt.compiler.pipeline import CompilationPipeline
from orionbelt.models.query import QueryObject, QuerySelect

model_yaml = """
version: "1.0"
dataObjects:
  Orders:
    code: ORDERS
    columns:
      Price: { code: PRICE, abstractType: float }
      Country: { code: COUNTRY, abstractType: string }
dimensions:
  Country:
    dataObject: Orders
    column: Country
    resultType: string
measures:
  Total Revenue:
    resultType: float
    aggregation: sum
    expression: "{[Orders].[Price]}"
"""

loader = TrackedLoader()
raw, source_map = loader.load_string(model_yaml)
resolver = ReferenceResolver()
model, result = resolver.resolve(raw, source_map)

query = QueryObject(select=QuerySelect(dimensions=["Country"], measures=["Total Revenue"]))
pipeline = CompilationPipeline()
output = pipeline.compile(query, model, "postgres")
print(output.sql)

Output:

SELECT
  "Orders"."COUNTRY" AS "Country",
  CAST(SUM("Orders"."PRICE") AS NUMERIC(18, 2)) AS "Total Revenue"
FROM ORDERS AS "Orders"
GROUP BY "Orders"."COUNTRY"

No env file needed — the compilation pipeline is stateless.

Option D: Docker

Stage 1 — Zero-config start (models loaded later via API or UI):

docker run -p 8080:8080 ralforion/orionbelt-api

Open http://localhost:8080/docs to explore the API.

Stage 2 — Realistic setup with docker compose:

# docker-compose.yml
services:
  api:
    image: ralforion/orionbelt-api:1.8.1
    ports: ["8080:8080"]
    env_file: .env
    volumes:
      - ./models:/app/models:ro
    environment:
      MODEL_FILE: /app/models/my-model.obml.yml

  ui:
    image: ralforion/orionbelt-ui:1.8.1
    ports: ["7860:7860"]
    environment:
      API_BASE_URL: http://api:8080

docker compose up -d

See .env.template for the full environment variable reference.

Docker notes:

• API_SERVER_HOST is already 0.0.0.0 inside the container — no override needed.
• MCP via stdio does not work in Docker. Use the MCP HTTP client for containerized deployments.
• Mount models to /app/models (or any path) and set MODEL_FILE to pre-load on startup.
• For production, pin a version tag (:1.8.1) rather than :latest.

Claude Desktop / MCP

The MCP server is a separate thin client that delegates to the REST API:

orionbelt-semantic-layer-mcp

Add to your Claude Desktop claude_desktop_config.json:

{
  "mcpServers": {
    "orionbelt": {
      "command": "uvx",
      "args": ["orionbelt-semantic-layer-mcp"]
    }
  }
}

Also works with Copilot, Cursor, and Windsurf. See the MCP repo for full setup options.

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Why OrionBelt?

	OrionBelt	dbt Semantic Layer	Cube	Malloy
Model format	YAML-only (OBML)	Python + YAML	JavaScript	Custom DSL
SQL generation	AST-based (injection-safe)	String templates	String templates	Compiler
Multi-dialect	8 dialects, no runtime lock-in	dbt Cloud required	Cube Cloud or self-host	BigQuery-focused
Multi-fact queries	Star Schema + CFL planner (fan-trap prevention)	Limited	Pre-aggregations	Automatic joins
Integration surface	REST API + MCP + Gradio UI	dbt Cloud API	REST + GraphQL	VS Code extension
Deployment	Self-host anywhere, single binary	SaaS (Cloud)	SaaS or self-host	Library
License	BSL 1.1 (converts to Apache 2.0)	Apache 2.0	AGPL / proprietary	MIT

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Features

Semantic Modeling

• OBML Format — YAML-based semantic models with data objects, dimensions, measures, metrics, and joins
• Cross-Schema Queries — model data objects across multiple databases and schemas in a single model
• Static Model Filters — mandatory WHERE conditions baked into the model, auto-applied with join extension
• OBSL Graph & SPARQL — RDF graph export and read-only SPARQL querying for every loaded model
• OSI Interoperability — bidirectional conversion between OBML and Open Semantic Interchange format

SQL Compilation

• 8 SQL Dialects — BigQuery, ClickHouse, Databricks, Dremio, DuckDB/MotherDuck, MySQL, Postgres, Snowflake
• AST-Based Generation — custom SQL AST ensures correct, injection-safe SQL (not string templates)
• Star Schema & CFL — automatic join resolution with Composite Fact Layer for multi-fact queries
• Data Types & Precision — automatic CAST wrapping with dialect-specific type rendering and precision clamping
• Display Formatting — number format patterns (#,##0.00, 0.00%) on measures/metrics with locale-aware rendering
• Timezone Settings — auto-detect database session timezone with defaultTimezone fallback and ISO 8601 serialization
• sqlglot Validation — post-generation syntax check across all supported dialects

Integration Surface

• REST API — FastAPI endpoints for model management, validation, compilation, and execution
• MCP Server — separate thin client for Claude, Copilot, Cursor, Windsurf
• AI Integrations — LangChain, OpenAI Agents SDK, CrewAI, Google ADK, Vercel AI SDK, n8n, ChatGPT
• Gradio UI — interactive web interface for model editing, query testing, and ER diagrams
• DB-API 2.0 + Flight SQL — PEP 249 drivers and Arrow Flight SQL server for DBeaver, Tableau, Power BI

Developer Experience

• Source-Position Errors — validation errors report exact YAML line and column
• ER Diagrams — interactive Mermaid diagrams with zoom and download (MD/PNG/Turtle)
• Session Management — TTL-scoped sessions with thread-safe model isolation
• JSON Schema — full OBML and query schema for IDE autocompletion (yaml-language-server)

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Example

Define a Semantic Model (OBML)

# yaml-language-server: $schema=https://raw.githubusercontent.com/ralfbecher/orionbelt-semantic-layer/main/schema/obml-schema.json
version: "1.0"
dataObjects:
  Customers:
    code: CUSTOMERS
    database: WAREHOUSE
    schema: PUBLIC
    columns:
      Customer ID: { code: CUSTOMER_ID, abstractType: string }
      Country:     { code: COUNTRY, abstractType: string }

  Orders:
    code: ORDERS
    database: WAREHOUSE
    schema: PUBLIC
    columns:
      Order Customer ID: { code: CUSTOMER_ID, abstractType: string }
      Price:             { code: PRICE, abstractType: float }
      Quantity:          { code: QUANTITY, abstractType: int }
    joins:
      - joinType: many-to-one
        joinTo: Customers
        columnsFrom: [Order Customer ID]
        columnsTo: [Customer ID]

dimensions:
  Country:
    dataObject: Customers
    column: Country
    resultType: string

measures:
  Revenue:
    resultType: float
    aggregation: sum
    expression: "{[Orders].[Price]} * {[Orders].[Quantity]}"
    dataType: "decimal(18, 2)"

Compile via REST API

# Create a session
curl -s -X POST http://localhost:8080/v1/sessions | jq .session_id
# -> "a1b2c3d4"

# Load the model
curl -s -X POST http://localhost:8080/v1/sessions/a1b2c3d4/models \
  -H "Content-Type: application/json" \
  -d '{"model_yaml": "..."}' | jq .model_id
# -> "abcd1234"

# Compile a query
curl -s -X POST http://localhost:8080/v1/sessions/a1b2c3d4/query/sql \
  -H "Content-Type: application/json" \
  -d '{"model_id":"abcd1234","query":{"select":{"dimensions":["Country"],"measures":["Revenue"]}},"dialect":"postgres"}' \
  | jq -r .sql

Generated SQL (Postgres)

SELECT
  "Customers"."COUNTRY" AS "Country",
  CAST(SUM("Orders"."PRICE" * "Orders"."QUANTITY") AS NUMERIC(18, 2)) AS "Revenue"
FROM WAREHOUSE.PUBLIC.ORDERS AS "Orders"
LEFT JOIN WAREHOUSE.PUBLIC.CUSTOMERS AS "Customers"
  ON "Orders"."CUSTOMER_ID" = "Customers"."CUSTOMER_ID"
GROUP BY "Customers"."COUNTRY"

Change dialect to bigquery, clickhouse, databricks, dremio, duckdb, mysql, or snowflake for dialect-specific SQL.

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Gradio UI

• SQL Compiler — side-by-side OBML model and query editors with syntax highlighting, 8 dialect selector, one-click compilation with formatted SQL output and query explain
• Query Execution — execute compiled queries against a connected database, view results with locale-aware number formatting, response metadata panel, TSV download and clipboard copy (requires QUERY_EXECUTE=true)
• ER Diagram — interactive Mermaid ER diagram with zoom, column toggle, and download (MD/PNG/Turtle)
• Editor Toolbar — clear, undo, redo, upload, download, and copy buttons on all code editors
• OSI Import/Export — convert between OBML and OSI formats
• Dark/Light Mode — toggle via header button, state persisted across sessions

Embedded mode — the UI is mounted at /ui on the API server:

pip install orionbelt-semantic-layer && orionbelt-api
# -> UI at http://localhost:8000/ui

Standalone mode — run API and UI as separate processes:

orionbelt-api                                              # API on :8000
orionbelt-ui                                               # UI on :7860 (connects to API on :8000)
API_BASE_URL=http://remote-api:8080 orionbelt-ui           # point UI to a remote API

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Documentation

Topic	Link
Full docs site	ralforion.com/orionbelt-semantic-layer
Installation	getting-started/installation
Quick Start	getting-started/quickstart
Docker & Deployment	getting-started/docker
Development	getting-started/development
OBML Model Format	guide/model-format
Query Language	guide/query-language
SQL Dialects	guide/dialects
Period-over-Period Metrics	guide/period-over-period
Compilation Pipeline	guide/compilation
OBSL Graph & SPARQL	guide/obsl
Gradio UI	guide/ui
AI Integrations	guide/integrations
OSI Interoperability	guide/osi
REST API Endpoints	api/endpoints
DB-API Drivers & Flight SQL	drivers
Architecture	reference/architecture
Configuration	reference/configuration
Sales Model Walkthrough	examples/sales-model
Multi-Dialect Output	examples/multi-dialect
Multi-Fact: Sales & Returns	examples/multi-fact
TPC-DS Benchmark	examples/tpcds
Quickstart Notebook	examples/quickstart.ipynb

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Status & Roadmap

Status	Area
Shipped	8 SQL dialects, REST API, MCP server, Gradio UI, DB-API drivers, Flight SQL, OBSL/SPARQL, OSI interop, AI integrations (LangChain, CrewAI, ADK, etc.), model inheritance & extends, data types & numerical precision, timezone settings, grain & filter context overrides
In progress	Additional dialects, CLI tool
Planned	Authentication & API tokens, CLI for automation & CI/CD, DDL view generation (CREATE VIEW from queries), additional BI tool integrations

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Companion Project

OrionBelt Analytics

An ontology-based MCP server that analyzes relational database schemas and generates RDF/OWL ontologies. Together with OrionBelt Semantic Layer, it enables AI assistants to navigate your data landscape through ontologies and compile safe, dialect-aware analytical SQL.

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Development

Contributing to OrionBelt or running from source:

git clone https://github.com/ralfbecher/orionbelt-semantic-layer.git
cd orionbelt-semantic-layer
uv sync                           # install all deps (dev, docs, ui, flight, drivers)
uv run orionbelt-api              # start API on :8000

# Quality
uv run pytest                     # run tests
uv run ruff check src/            # lint
uv run ruff format src/ tests/    # format
uv run mypy src/                  # type check

# Docs
uv sync --extra docs && uv run mkdocs serve  # docs on :8080

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License

Copyright 2025 RALFORION d.o.o.

Licensed under the Business Source License 1.1. The Licensed Work will convert to Apache License 2.0 on 2030-03-16.

By contributing to this project, you agree to the Contributor License Agreement.

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