osi-orionbelt

Bidirectional converter between OBML (OrionBelt Markup Language) semantic models and OSI (Open Semantic Interchange), the open standard for portable semantic models (metrics, dimensions, relationships).

This package is licensed under Apache-2.0 and may be used freely. It is the OrionBelt converter in the OSI converter ecosystem. The canonical source is developed in the orionbelt-semantic-layer repository (under packages/osi-orionbelt) and published to PyPI from there; file issues and contributions upstream.

Requirements

• Python 3.12+
• uv (recommended) or pip

Install

pip install osi-orionbelt

Optional deep OBML semantic validation (cycles, duplicate names, invalid refs) via the full OrionBelt engine:

pip install "osi-orionbelt[obml-validation]"

Without that extra, OBML validation runs JSON-schema checks only and emits a warning for the deeper semantic pass.

CLI

A single osi-orionbelt command with two subcommands (mirroring osi-dbt):

osi-orionbelt obml-to-osi -i model.obml.yaml -o model.osi.yaml
osi-orionbelt osi-to-obml -i model.osi.yaml -o model.obml.yaml

-i/--input and -o/--output are required. Each subcommand prints conversion warnings and a validation summary to stderr, and exits non-zero when the produced document fails schema validation (unless --no-validate). Run osi-orionbelt --help or osi-orionbelt obml-to-osi --help for the full option list.

Python API

import yaml
from osi_orionbelt import OBMLtoOSI, OSItoOBML, validate_osi

obml = yaml.safe_load(open("model.obml.yaml"))
osi = OBMLtoOSI(obml, "sales", "Sales model").convert()
result = validate_osi(osi)
assert result.valid

obml_again = OSItoOBML(osi).convert()

Vendor extensions

OSI custom_extensions carry vendor-tagged payloads. This converter:

• emits OrionBelt/OBML-proprietary data under the ORIONBELT vendor on OBML to OSI (OBML-only filters, settings, owner, refresh, type info, etc.);
• stashes OSI-native fields that OBML can't represent (unique keys, field labels, leftover ai_context) under the OSI vendor when going OSI to OBML, restoring them to first-class OSI fields on the way back;
• preserves third-party vendor extensions verbatim (e.g. SNOWFLAKE, DBT, SALESFORCE, GOODDATA) at the model, dataset, field, and measure/metric levels, so a full OSI to OBML to OSI roundtrip keeps the original vendor and data. OSI has no separate dimension entity, so an OBML dimension's foreign extensions surface on its OSI field.

Legacy COMMON / OBSL tags from earlier converter versions are still accepted on read.

Limitations / unsupported constructs

Some OBML constructs have no native OSI equivalent and are carried in vendor custom_extensions (obml_* payloads) so they round-trip without loss back to OBML, but are not interpreted by other OSI consumers:

• Many-to-many joins - represented in OBML join cardinality; flagged on export.
• Named secondary join paths - OBML's multiple join paths between the same pair of objects are an OBML-specific topology feature.
• OSI metrics with no OBML representation - a metric whose only expression is in a non-SQL dialect (MDX, TABLEAU, MAQL), or whose SQL expression cannot be decomposed into OBML measures/metrics, is not dropped: the original OSI metric is preserved verbatim in a model-level OSI-vendor custom_extension (obml_unconverted_metrics) and re-emitted on OBML to OSI, so the OSI to OBML to OSI roundtrip stays lossless. A LOSSY: warning is raised for each such metric because it is not queryable through OBML. SQL expressions in the ANSI_SQL, OSSIE_SQL_2026, SNOWFLAKE, and DATABRICKS dialects are all read on import.

OSI v0.1.x inputs are accepted on read via a legacy normalization shim; output targets OSI v0.2.0.dev0.

See osi_obml_mapping_analysis.md for the full OBML <-> OSI core-spec mapping.

Development

uv sync          # install
uv run pytest    # run the test suite (includes a TPC-DS baseline)
uv run ruff check && uv run mypy src/osi_orionbelt