# Data Contract

> A rule or precondition that data exchanged between parties has declared fields, types, nullability and meaning.

Record: `architecture:data-contract`
Kind: constraint
Layer: [Contracts Core](https://banes-lab.com/records/layer/contracts-core.md)
Severity: mandatory
Scope: data, message, persistence, integration
Canonical: https://banes-lab.com/ontology#architecture-data-contract

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Service Contract](https://banes-lab.com/records/architecture/service-contract.md) and before [Schema Contract](https://banes-lab.com/records/architecture/schema-contract.md).

## Repair

- Refactored by: Add DTO, Add Schema, Normalize Field Semantics
- Detected by: data validation failures, schema mismatch
- Violated by: untyped maps, implicit fields, undocumented nullability
- Measured by: schema conformance rate
- Enforced by: schema registry, validation gates

## Requires

- [Schema](https://banes-lab.com/records/lexicon/schema.md)
- [Type Safety](https://banes-lab.com/records/architecture/type-safety.md)
- [Semantic Consistency](https://banes-lab.com/records/architecture/semantic-consistency.md)

## Reinforces

- [Interoperability](https://banes-lab.com/records/architecture/interoperability.md)
- [Data Quality](https://banes-lab.com/records/lexicon/data-quality.md)

## Enables

- [Schema Evolution](https://banes-lab.com/records/lexicon/schema-evolution.md)

## Conflicts with

- [Schema Drift](https://banes-lab.com/records/architecture/schema-drift.md)

## In tension with

- [Flexible Ingestion](https://banes-lab.com/records/lexicon/flexible-ingestion.md)

## Tensions

- [Data Contract / Flexible Ingestion](https://banes-lab.com/records/tension/data-contract-flexible-ingestion.md)

## Severity

- [mandatory](https://banes-lab.com/records/vocabulary/severity-mandatory.md)

## Category

- [Contracts / Interfaces / Compatibility](https://banes-lab.com/records/architecture-category/contracts-interfaces-compatibility.md)

## Reinforced by

- [Schema Contract](https://banes-lab.com/records/architecture/schema-contract.md)
- [Schema Validation](https://banes-lab.com/records/architecture/schema-validation.md)

## Required by

- [Canonical Data Model](https://banes-lab.com/records/architecture/canonical-data-model.md)

## Linked from

- [Anti-patterns](https://banes-lab.com/ontology/principles/architecture-category-anti-patterns.md)
- [Contracts / Interfaces / Compatibility](https://banes-lab.com/ontology/principles/architecture-category-contracts-interfaces-compatibility.md)
- [Schema / Canonical Data / Semantics](https://banes-lab.com/ontology/principles/architecture-category-schema-canonical-data-semantics.md)
- [Contracts / Interfaces / Compatibility](https://banes-lab.com/ontology/lexicon/lexicon-category-contracts-interfaces-compatibility.md)
- [Core Vocabulary](https://banes-lab.com/ontology/lexicon/lexicon-category-core-vocabulary.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)