OMLE

Open Machine Learning Exchange — an open, schema-aware interchange format for classical machine learning inference.

OMLE provides a compact binary format (protobuf) for representing trained ML models and their preprocessing and postprocessing pipelines. It preserves model semantics at a level practical for interoperability, conversion, validation, and deployment-oriented inference across major ML ecosystems.

Why OMLE?

Classical ML has an interoperability gap:

• PMML is semantically rich but XML-based, verbose, and no meaningful updates for many years.
• ONNX-ML has poor support for classical ML semantics. It lacks schema-level concepts like feature binding, missing/invalid/outlier handling, measure levels, and value domains.
• Framework-native formats (pickle, joblib, XGBoost JSON, LightGBM text) are not portable and carry security risks.

OMLE fills this gap with a modern binary format that combines PMML's semantic richness with ONNX's operational pragmatism, under a permissive license.

Design

OMLE uses a hybrid representation:

• Logical schema — named features and targets with types, measure levels, value domains, and preprocessing policies (missing, invalid, outlier handling)
• Graph nodes — a DAG of named operators spanning preprocessing, model scoring, and postprocessing
• Structured model bodies — dedicated proto messages for classical ML families where preserving high-level semantics matters

Data Model

Every named value in the graph has shape [N, ...], where N is the leading row dimension. The graph operates on a namespace of named tensors — nodes consume named values and produce new named values. Structured implementations use positional indexing into a flat slot space derived from their input list.

Expression DSL

OMLE includes an elementwise expression sub-DSL for per-column derived computations. Expressions operate on [N] columns using a versioned set of 61 primitives (arithmetic, comparison, logical, math, conditional, null handling, string, date, type conversion, value mapping). The expression language is separate from the graph operator set — graph nodes handle structurally interesting operations, expressions handle elementwise math.

Scope Isolation

CompositeNode introduces local namespaces for subgraph isolation. Internal nodes only see names explicitly passed as inputs — no transitive visibility into enclosing scopes. This enables clean composition of preprocessing pipelines and multi-model architectures without name collisions.

Installation

The omle Python package is the reference implementation: the in-memory IR, protobuf serialization, validation, and the omle CLI.

# Core SDK (IR types, protobuf I/O, validation, CLI)
pip install omle

# With individual components
pip install "omle[convert]"   # converters (scikit-learn, Spark ML, XGBoost, LightGBM, CatBoost)
pip install "omle[runtime]"   # C++ inference runtime
pip install "omle[viewer]"    # Jupyter / browser DAG viewer

# Everything
pip install "omle[all]"

Requires Python 3.10+. protobuf is the only required dependency.

Quick Start

import omle

# Load a model — format is inferred from the extension
# (.omle / .pb / .bin → protobuf, .json → JSON)
model = omle.load("model.omle")

# Validate against structural rules and the operator/function registries
result = omle.validate(model)
if not result.is_valid:
    print(result)

# Inspect
print(model.metadata.format_version)
for fw in model.metadata.source_frameworks:
    print(fw.name, fw.version, fw.role)
for node in model.nodes:
    print(node.name, f"{node.domain}.{node.op}")

# Round-trip to JSON for diffing or hand-editing
omle.save(model, "model.json")

Converting a trained model requires omle-convert:

from omle import export_omle

# scikit-learn, XGBoost, LightGBM, CatBoost — pass the fitted model
export_omle(sklearn_pipeline, "model.omle", X=X_test)

# Spark ML — pass a fitted PipelineModel; dataset supplies verification and sample rows
export_omle(pipeline_model, "spark_model.omle", dataset=train_df)

Command-Line Interface

The omle CLI provides tools for working with model files:

# Validate a model file
omle validate model.omle
omle validate model.omle --no-registry

# Inspect a model's structure
omle inspect model.omle
omle inspect model.omle --section nodes
omle inspect model.omle --section metadata
omle inspect model.omle --json

# Open the interactive DAG viewer in a browser (requires omle-viewer)
omle view model.omle

# Convert a model to OMLE format (requires omle-convert).
# The source framework is auto-detected from the file contents or extension.
omle convert model.joblib    output.omle   # scikit-learn
omle convert saved_pipeline/ output.omle   # Spark ML
omle convert model.json      output.omle   # XGBoost JSON (or CatBoost JSON)
omle convert model.txt       output.omle   # LightGBM
omle convert model.cbm       output.omle   # CatBoost native

omle convert forwards all arguments to omle-convert; see its README for the full option set.

Reference

• Specification — proto schema, registries, versioning
• Operator and function reference — every ML model family, feature operator and expression primitive, generated from the registries

Ecosystem

Converter Status

Provided by omle-convert:

Contributing

OMLE is in active development. The proto schema and registries are stabilizing toward a v1 release. See CONTRIBUTING.md for development setup and the checks a change needs to pass, and CODE_OF_CONDUCT.md for community expectations.

Contributions are welcome in:

• Converter implementations
• Runtime implementations
• Validation tooling
• Documentation and specification refinements

License

Apache License v2.0