ohdsi-cohort-schemas 0.3.1

Pydantic models for validating OHDSI/Circe cohort definition schemas

OHDSI Cohort Schemas

Pydantic models for validating OHDSI/Circe cohort definition schemas. This library provides comprehensive type-safe validation for OHDSI cohort expressions, enabling:

• IDE Support: Full autocompletion and type checking for cohort definitions
• Schema Validation: Catch errors before sending to WebAPI
• Documentation: Living documentation via Pydantic models
• Interoperability: Consistent schema validation across tools

Attribution: This library is based on the cohort expression schema from the OHDSI Circe project. Test data and schema structures are derived from the official Circe backend test suite to ensure compatibility with OHDSI standards.

Installation

pip install ohdsi-cohort-schemas

Quick Start

from ohdsi_cohort_schemas import CohortExpression, validate_schema_only, validate_with_warnings

# Quick schema validation (fast, Pydantic-only)
try:
    cohort = validate_schema_only(cohort_json)
    print("✅ Valid schema!")
except ValidationError as e:
    print(f"❌ Schema errors: {e}")

# Full validation with business logic checks (comprehensive)
cohort, warnings = validate_with_warnings(cohort_json)
print("✅ Valid cohort definition!")
if warnings:
    print("⚠️ Warnings:")
    for warning in warnings:
        print(f"  - {warning.message}")

WebAPI Format Support

This library supports WebAPI camelCase format in addition to the native Circe mixed-case format. This enables seamless integration with OHDSI WebAPI clients.

Format Differences

• Circe Format: Mixed case (PascalCase + camelCase + ALL_CAPS)

  {
    "ConceptSets": [{"id": 1, "expression": {"items": [{"concept": {"CONCEPT_ID": 123}}]}}],
    "PrimaryCriteria": {"CriteriaList": [{"ConditionOccurrence": {"CodesetId": 1}}]}
  }
  

• WebAPI Format: Consistent camelCase

  {
    "conceptSets": [{"id": 1, "expression": {"items": [{"concept": {"conceptId": 123}}]}}],
    "primaryCriteria": {"criteriaList": [{"conditionOccurrence": {"codesetId": 1}}]}
  }
  

WebAPI Validation Functions

from ohdsi_cohort_schemas import (
    validate_webapi_schema_only,
    validate_webapi_with_warnings,
    validate_webapi_strict,
    webapi_to_circe_dict,
    circe_to_webapi_dict
)

# Validate WebAPI camelCase format directly
cohort = validate_webapi_schema_only(webapi_json)

# Get warnings for WebAPI format
cohort, warnings = validate_webapi_with_warnings(webapi_json)

# Strict validation (raises on warnings)
cohort = validate_webapi_strict(webapi_json)

# Format conversion
circe_format = webapi_to_circe_dict(webapi_json)
webapi_format = circe_to_webapi_dict(circe_json)

Building Cohorts Programmatically

from ohdsi_cohort_schemas import CohortExpression, ConceptSet, ConceptSetItem, Concept

# Define a concept set
concept = Concept(
    concept_id=201826,
    concept_name="Type 2 diabetes mellitus",
    standard_concept="S",
    concept_code="44054006",
    concept_class_id="Clinical Finding",
    vocabulary_id="SNOMED",
    domain_id="Condition"
)

concept_set_item = ConceptSetItem(
    concept=concept,
    include_descendants=True,
    include_mapped=False,
    is_excluded=False
)

concept_set = ConceptSet(
    id=0,
    name="Type 2 Diabetes",
    expression=ConceptSetExpression(items=[concept_set_item])
)

# Build a complete cohort expression
cohort_expression = CohortExpression(
    concept_sets=[concept_set],
    primary_criteria=...,  # Define primary criteria
    inclusion_rules=[],    # Optional inclusion rules
    censoring_criteria=[]  # Optional censoring criteria
)

Features

Complete Schema Coverage

• ✅ ConceptSets - Medical concept definitions with descendants
• ✅ PrimaryCriteria - Index event definitions
• ✅ InclusionRules - Additional filtering criteria
• ✅ CensoringCriteria - Observation period requirements
• ✅ All Criteria Types - Conditions, drugs, procedures, measurements, etc.
• ✅ Time Windows - Complex temporal relationships
• ✅ Demographics - Age, gender, race, ethnicity filters

Validation Features

• Dual Validation Modes: Fast schema-only validation or comprehensive business logic validation
• Schema Validation: Pure Pydantic validation for structure and types
• Business Logic Validation: Semantic checks for logical consistency and OHDSI best practices
• Type Safety: Full static type checking with mypy
• Runtime Validation: Comprehensive Pydantic validation
• Custom Validators: Domain-specific validation rules
• Error Messages: Clear, actionable validation errors
• JSON Schema: Generate JSON schemas for other tools

Documentation

Core Models

CohortExpression

The root model representing a complete cohort definition:

class CohortExpression(BaseModel):
    concept_sets: List[ConceptSet]
    primary_criteria: PrimaryCriteria
    qualified_limit: Optional[Limit] = None
    expression_limit: Optional[Limit] = None
    inclusion_rules: List[InclusionRule] = []
    end_strategy: Optional[EndStrategy] = None
    censoring_criteria: List[CensoringCriteria] = []
    collapse_settings: Optional[CollapseSettings] = None
    censor_window: Optional[CensorWindow] = None

ConceptSet

Defines reusable groups of medical concepts:

class ConceptSet(BaseModel):
    id: int
    name: str
    expression: ConceptSetExpression

class ConceptSetExpression(BaseModel):
    items: List[ConceptSetItem]

class ConceptSetItem(BaseModel):
    concept: Concept
    include_descendants: bool = True
    include_mapped: bool = False
    is_excluded: bool = False

Criteria Types

Support for all OMOP domain criteria:

• ConditionOccurrence - Medical conditions
• DrugExposure - Medication exposures
• DrugEra - Continuous drug exposure periods
• ProcedureOccurrence - Medical procedures
• Measurement - Lab values and vital signs
• Observation - Clinical observations
• DeviceExposure - Medical device usage
• Death - Death events
• VisitOccurrence - Healthcare encounters
• VisitDetail - Detailed visit information
• ObservationPeriod - Data availability periods
• Specimen - Biological specimen collection

Library Scope

This library focuses specifically on cohort expression validation - the clinical logic that defines patient selection criteria. It validates the expression portion of cohort definitions, which contains:

• ConceptSets - Medical concept definitions
• PrimaryCriteria - Index event definitions
• InclusionRules - Additional filtering criteria
• CensoringCriteria - Observation period requirements

What This Library Does NOT Handle

This library intentionally does not handle WebAPI metadata such as:

• Cohort metadata (id, name, description)
• Permission management (hasWriteAccess, tags)
• User tracking (createdBy, modifiedBy)
• Timestamps (createdDate, modifiedDate)

These concerns are handled by API client libraries (like ohdsi-webapi-client) that focus on the full WebAPI response structure while using this library for the clinical validation of the expression field.

Integration Example

# WebAPI client handles full response
cohort_response = {
    "id": 123,
    "name": "My Cohort",
    "hasWriteAccess": true,
    "expression": {
        "ConceptSets": [...],     # ← This library validates this part
        "PrimaryCriteria": {...}  # ← And this part
    }
}

# Extract and validate just the expression
from ohdsi_cohort_schemas import validate_webapi_schema_only
validated_expression = validate_webapi_schema_only(cohort_response["expression"])

JSON Format Support

This library supports two different JSON field naming conventions, reflecting the different contexts where cohort definitions are used:

Database Format (ALL_CAPS)

Used by Circe backend test data and internal cohort processing:

{
  "concept": {
    "CONCEPT_ID": 201826,
    "CONCEPT_NAME": "Type 2 diabetes mellitus",
    "VOCABULARY_ID": "SNOMED"
  }
}

WebAPI Format (camelCase)

Used by OHDSI WebAPI JSON responses and web applications:

{
  "concept": {
    "conceptId": 201826,
    "conceptName": "Type 2 diabetes mellitus", 
    "vocabularyId": "SNOMED"
  }
}

Why Two Formats?

• Circe Backend Test Data: Uses ALL_CAPS because it matches OMOP CDM database column names (which are traditionally UPPERCASE in SQL databases)

• WebAPI JSON Responses: Uses camelCase because it follows standard JSON/JavaScript conventions for web APIs

• Different Purposes:

  • Circe: Internal cohort definition processing (matches database schema)
  • WebAPI: External API communication (matches web standards)

The library provides separate validation functions for each format to ensure seamless integration with both contexts.

Validation Examples

WebAPI Format Validation (camelCase)

For WebAPI responses and web application JSON:

from ohdsi_cohort_schemas import validate_webapi_schema_only, validate_webapi_with_warnings

# Fast schema validation for WebAPI format
try:
    cohort = validate_webapi_schema_only(webapi_json)  # camelCase format
    print("✅ Valid WebAPI schema!")
except ValidationError as e:
    print(f"❌ Schema errors: {e}")

# Full validation with business logic checks
result = validate_webapi_with_warnings(webapi_json)
if result.is_valid:
    print("✅ Valid cohort definition!")
    if result.warnings:
        print("⚠️ Warnings:")
        for warning in result.warnings:
            print(f"  - {warning}")
else:
    print("❌ Validation failed:")
    for error in result.errors:
        print(f"  - {error}")

Standard Validation Functions

The main validation functions work with the Circe mixed-case format:

from ohdsi_cohort_schemas import validate_schema_only, validate_with_warnings, validate_strict

# Fast schema validation
try:
    cohort = validate_schema_only(circe_json)
    print("✅ Valid schema!")
except ValidationError as e:
    print(f"❌ Schema errors: {e}")

# Validation with warnings for best practices
cohort, warnings = validate_with_warnings(circe_json)
print("✅ Valid cohort definition!")
if warnings:
    print("⚠️ Warnings:")
    for warning in warnings:
        print(f"  - {warning.message}")

# Strict validation - warnings treated as errors
try:
    cohort = validate_strict(circe_json)
    print("✅ Perfect cohort definition!")
except ValidationError as e:
    print(f"❌ Validation failed: {e}")

Advanced Business Logic Validation

from ohdsi_cohort_schemas import BusinessLogicValidator

# Custom validation with specific rules
validator = BusinessLogicValidator()
issues = validator.validate(cohort_json)

errors = [issue for issue in issues if issue.severity == 'error']
warnings = [issue for issue in issues if issue.severity == 'warning']

print(f"Found {len(errors)} errors and {len(warnings)} warnings")
for issue in errors:
    print(f"❌ {issue.rule}: {issue.message}")
for issue in warnings:
    print(f"⚠️ {issue.rule}: {issue.message}")

Direct Pydantic Validation

from ohdsi_cohort_schemas import CohortExpression
from pydantic import ValidationError

# Direct Pydantic validation (lowest-level approach)
try:
    cohort = CohortExpression.model_validate(cohort_json)
    print("✅ Valid schema!")
except ValidationError as e:
    print(f"❌ Schema errors:")
    for error in e.errors():
        print(f"  - {error['loc']}: {error['msg']}")

JSON Schema Generation

from ohdsi_cohort_schemas import CohortExpression

# Generate JSON schema for other tools
schema = CohortExpression.model_json_schema()

# Save for use in other languages/tools
import json
with open("cohort_schema.json", "w") as f:
    json.dump(schema, f, indent=2)

Test Data & Validation

Test Data Structure

Our comprehensive test suite uses official JSON examples from the OHDSI Circe project to ensure compatibility with real-world cohort definitions:

tests/resources/
├── checkers/                 # Business logic validation test cases
│   ├── *Correct.json        # Valid cohorts (should pass validation)
│   └── *Incorrect.json      # Invalid cohorts (should fail validation)
├── conceptset/              # Standalone concept set expressions
└── cohortgeneration/        # Complete cohort definitions

Test Categories

• Schema Validation Tests: All JSON files are validated against our Pydantic models
• Business Logic Tests: Files ending with Correct.json should pass all validation rules
• Negative Tests: Files ending with Incorrect.json should fail business logic validation
• Concept Set Tests: Standalone concept set expressions for testing concept-related logic

Data Source Attribution

The test data originates from the official Circe test resources, ensuring our validation logic handles the same edge cases and patterns that the official OHDSI tools encounter.

Note: We've removed _PREP.json and _VERIFY.json files from the original Circe test suite as these are used for database-level testing of SQL generation, not JSON schema validation. Our library focuses on validating cohort definition structure and business logic before database execution.

Contributing

We welcome contributions! Please see our Contributing Guide for details.

Attribution & License

Schema Source

This library implements Pydantic models for the cohort expression schema defined by the OHDSI Circe project. The schema structures, field definitions, and validation logic are derived from the official Circe backend to ensure full compatibility with OHDSI standards.

Test Data

The validation test suite uses official JSON examples from the Circe test resources to ensure our implementation correctly handles real-world cohort definitions.

OHDSI Ecosystem Compatibility

• License: Apache 2.0 (matching OHDSI ecosystem standards)
• Standards: Fully compatible with OHDSI WebAPI and ATLAS
• OMOP CDM: Supports the OMOP Common Data Model vocabulary standards
• Interoperability: Designed for seamless integration with other OHDSI tools

Acknowledgments

We gratefully acknowledge:

• OHDSI Collaborative for developing and maintaining the Circe cohort expression standards
• Pydantic for providing the validation framework
• OHDSI Community for the open-source ecosystem that makes this work possible

License

This project is licensed under the Apache License 2.0 - see the LICENSE file for details.