Implement a Schema-Specific XML Validator with Schematron Support

[Bergmann89]

In addition to the existing code generator, we propose implementing a generator that produces a strict XML validator tailored to a given schema. This validator would leverage a streaming approach using quick_xml event parsing and provide an additional layer of validation using XML schematron rules.

Rationale

Currently, the generated deserialization code is designed to be robust and tolerant of errors. However, a stricter validation mechanism is required to ensure that XML documents conform precisely to their schemas before deserialization or after serialization. A dedicated validator with schematron support would:

• Enforce strict schema validation before processing XML data.
• Validate additional business logic constraints via schematron rules.
• Improve data integrity and compliance with XML schema constraints.
• Offer an independent validation step that can be used standalone.

Proposed Approach

1. Streaming Validation Using quick_xml

   • Utilize the event-based parsing mechanism of quick_xml.
   • Validate elements, attributes, and structure in real-time as XML is parsed.
   • Minimize memory footprint by avoiding full document loading.

2. Integration with XML schematron

   • Support rule-based validation beyond structural checks.
   • Use XPath-based validation for conditional constraints and cross-element relationships.
   • Allow users to define schematron files alongside schemas for enhanced validation.

3. Integration with Code Generation

   • The validator should be schema-specific and generated alongside the existing code generator.
   • Ensure strict validation rules are enforced, while deserialization remains error-tolerant.
   • Provide validation hooks before deserialization and/or after serialization.

4. Usage Scenarios

   • Pre-deserialization Validation: Ensures the XML document strictly follows the schema and business rules before it is deserialized.
   • Post-serialization Validation: Confirms that the generated XML conforms to the expected structure and constraints after serialization.
   • Standalone Validation: Can be used independently for schema and schematron rule compliance testing.

Expected Outcome

• A lightweight and efficient XML validator for schema compliance and rule-based validation.
• Improved error handling by distinguishing between strict validation and lenient deserialization.
• Enhanced reliability of XML-based data processing with support for complex validation rules.