[FEATURE] Ontology Diff & Migration

[KaifAhmad1]

Treat ontology changes like database migrations: diff, analyze impact, and migrate safely over time.

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Where in the Codebase This Lives

• Main implementation goes into:
  • semantica/change_management/ (version manager, storage, change logs).
  • semantica/ontology/ (public API on the engine).
• Tests should extend the existing suites under:
  • tests/change_management/
  • tests/ontology/
• Keep everything under the existing semantica/ and tests/ trees; do not introduce new top‑level folders.

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Functional Overview

• Compares two ontology versions stored in Semantica.
• Produces a structured diff (added/removed/changed classes and properties).
• Generates a human‑readable migration and impact report.
• Optionally triggers validation jobs to check data against the new schema.

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Motivation and Benefits

• Enables safe ontology evolution in long‑lived enterprise systems.
• Adds version control and change tracking for schemas, not just data.
• Helps data teams understand exactly what breaks when a schema changes.
• Supports deployment automation and governance for semantic models.

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Existing Functionality to Leverage

Existing capabilities that this feature will reuse:

• Ontology
  • semantica/ontology/engine.py
    • High‑level operations for generating, validating, and exporting ontologies.
  • semantica/ontology/ontology_validator.py
    • Structural validation and hooks for symbolic reasoners.
  • semantica/ontology/ontology_evaluator.py
    • Evaluation of ontology quality and competency question coverage.
• Change management
  • semantica/change_management/ontology_version_manager.py
  • semantica/change_management/version_storage.py
  • semantica/change_management/change_log.py
  • semantica/change_management/managers.py
• Documentation and tests
  • docs/reference/ontology.md
  • docs/reference/change_management.md
  • tests/change_management/test_managers.py
  • tests/change_management/test_temporal_versioning.py
  • tests/change_management/test_change_log.py
  • tests/ontology/test_ontology_advanced.py

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New Capabilities to Implement

Ontology diff and migration should be implemented entirely within these existing modules:

• Diff computation
  • In semantica/change_management/ontology_version_manager.py:
    • Implement diff_ontologies(base, target) → Dict with added/removed/changed elements.
• Version loading
  • In semantica/ontology/engine.py and change_management/managers.py:
    • Provide helpers to fetch ontology versions as plain dicts suitable for diffing.
• Impact and migration report
  • In semantica/change_management/change_log.py (or nearby helper):
    • Generate structured migration reports from the diff, classifying changes as breaking, potentially breaking, or low‑risk.
• Optional validation hooks
  • Use OntologyValidator and GraphValidator (from semantica/kg/graph_validator.py) to:
    • Define validation jobs that check existing data against the new ontology.
• Public API
  • In semantica/ontology/engine.py:
    • Add compare_versions(...) that orchestrates version loading, diff computation, and report generation.
• Documentation and tests
  • Extend the docs and tests listed above with:
    • Examples and assertions for ontology diffs.
    • At least one realistic migration report scenario.

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Contributor Implementation Guide

1. Structured ontology diff

   • In change_management/ontology_version_manager.py:
     • Implement a function:
       • diff_ontologies(base: Dict[str, Any], target: Dict[str, Any]) -> Dict[str, Any]
     • The returned dict should contain lists such as:
       • added_classes, removed_classes, changed_classes
       • added_properties, removed_properties, changed_properties
     • Changes should include details (e.g. domain/range changed, label changed).

2. Version retrieval helpers

   • In ontology/engine.py and change_management/managers.py:
     • Provide utilities to load ontology versions (e.g. by version ID or tag) as plain dicts ready for diffing.

3. Impact analysis and reporting

   • In change_management/change_log.py (or a small helper in the same package):
     • Build a report generator that:
       • Accepts the diff structure.
       • Produces a markdown or JSON report listing:
         • Breaking changes.
         • Potentially breaking changes.
         • Low‑risk changes (e.g. labels only).
       • Optionally includes references to affected classes, properties, and mapped entities.

4. Optional validation jobs

   • Using OntologyValidator and GraphValidator:
     • For selected changes, create validation jobs that:
       • Check data instances against the new constraints.
       • Surface issues before or during deployment.

5. Public API surface

   • In ontology/engine.py:
     • Add a method such as:
       • compare_versions(self, base_id: str, target_id: str, **options)
     • This should orchestrate:
       • Version loading.
       • Diff computation.
       • Report generation.

6. Documentation

   • In docs/reference/change_management.md:
     • Add an “Ontology Diff & Migration” section with:
       • A code example calling OntologyEngine.compare_versions.
       • Explanation of the report format.

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Ready‑to‑Ship Criteria

• There is a public API to compare two ontology versions and obtain:
  • A machine‑readable diff structure.
  • A human‑readable migration report.
• Change management tests cover:
  • Basic diff scenarios (class/property added/removed/changed).
  • Report generation for at least one realistic example.
• Ontology docs clearly show how to use the diff and migration capabilities.