type: object
description: |
  Source document reference. Produced by tracing the graph edges used for
  retrieval back to the documents they were extracted from.
properties:
  uri:
    type: string
    description: Source document URI
    example: urn:document:5a90a175-9906-4dcb-b482-a8c1b6cbf9e0
  title:
    type: string
    description: Document title (empty when the document has none)
    example: Quantum Mechanics Primer
required:
  - uri