Data Model Layer Skill

Layer Number: 07 Specification: Metadata Model Spec v0.7.0 Purpose: Defines logical data structures using JSON Schema Draft 7, specifying entities, properties, validation rules, and data governance.

Layer Overview

The Data Model Layer captures logical data structures:

• SCHEMAS - Object, array, string, numeric schemas
• VALIDATION - Type constraints, required fields, patterns, ranges
• COMPOSITION - Schema combinations (allOf, anyOf, oneOf, not)
• GOVERNANCE - Data classification, PII, retention policies
• INTEGRATION - Links to business objects, database tables, API operations

This layer uses JSON Schema Draft 7 (industry standard) with custom extensions for cross-layer traceability.

Central Entity: The ObjectSchema (defining an object structure) is the core modeling unit.

Entity Types

Core JSON Schema Entities (17 entities)

When to Use This Skill

Activate when the user:

• Mentions "data model", "schema", "JSON Schema", "data structure"
• Wants to define object structures, properties, or validation rules
• Asks about data types, constraints, or data governance
• Needs to model entities like User, Order, Product, etc.
• Wants to link data models to APIs or databases

Cross-Layer Relationships

Outgoing (Data Model → Other Layers):

• x-business-object-ref → Business Layer (what business concept does this represent?)
• x-database → Datastore Layer (how is this stored physically?)
• x-data-governance → Security Layer (classification, PII, retention)
• x-apm-data-quality-metrics → APM Layer (data quality monitoring)

Incoming (Other Layers → Data Model):

• API Layer → Data Model (request/response schemas via $ref)
• UX Layer → Data Model (form validation rules)
• Testing Layer → Data Model (input constraints for test partitioning)

Validation Best Practices

1. Required fields - Use required array for mandatory properties
2. Type validation - Always specify type (object, array, string, number, etc.)
3. Format validation - Use format for email, uuid, date-time, uri, etc.
4. Range validation - Use min/max for numbers, minLength/maxLength for strings
5. Pattern validation - Use pattern for regex validation (e.g., phone numbers)
6. Data governance - Always add x-data-governance for sensitive data
7. Reusability - Use $ref to reference shared schemas

Common Commands

# Add object schema
dr add data_model object-schema --name "User" --property type=object

# List data models
dr list data_model object-schema

# Validate data model layer
dr validate --layer data_model

# Export as JSON Schema
dr export --layer data_model --format json-schema

Example: User Schema

id: data_model.object-schema.user
name: "User Schema"
type: object-schema
properties:
  type: object
  required: [id, email, username]
  properties:
    id:
      type: string
      format: uuid
      description: "Unique user identifier"
    email:
      type: string
      format: email
      description: "User email address"
      x-data-governance:
        classification: confidential
        pii: true
    username:
      type: string
      minLength: 3
      maxLength: 50
      pattern: "^[a-zA-Z0-9_-]+$"
    created_at:
      type: string
      format: date-time
    roles:
      type: array
      items:
        type: string
      description: "User role assignments"
  x-business-object-ref: business.actor.user
  x-database:
    table: users
    schema: public

Pitfalls to Avoid

• ❌ Missing type field (validation will fail)
• ❌ Not marking PII/sensitive data with governance
• ❌ Overly complex schemas (break into smaller reusable schemas)
• ❌ Not using $ref for shared definitions
• ❌ Missing cross-layer links to business and database layers