openapi: 3.0.3
info:
  title: 'Example'
  version: '1.0.0'

externalDocs:
  # Reference to the base document
  description: 'ETSI ES 203 647 ...'
  url: 'https://rest.etsi.org'

paths:
[...]

components:
  schemas:
    ResourceData:
      # Structured type
      type: object
      properties:
        # Property name
        id:
          # Property type
          type: string
        size:
          type: string
          enum:
            # Set of allowed values
            - big
            - bigger
            - biggerer
          # Default value for non-required property
          default: big
        created:
          # Date-time value encoded as string
          type: string
          format: date-time
      required:
        # Set of required properties
        - id
[...]

Package ExampleAPI {
    Import all from Standard;
    Import all from HTTP.MessageBased; 
    
    //From Example API specification    
    Type ResourceData extends Body (
      id of type String,
      //can be skipped
      optional ^size of type Integer, 
      //can be skipped 
      optional created of type String  
    );
}