paths:
    /:
     get:
        # ...
    put:
      summary: ...
      parameters:
        - name: id
          in: path
          description: ID of the book you will like to update
          required: true
          schema:
            type: integer
            format: int64
      requestBody:
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/Book"
        description: JSON payload of the book that needs to be updated
        required: true
      # TODO: response structure 

components:
  schemas:
    Book:
      type: object
      required:
        - title
        - pages
      properties:
        title:
          type: string
          example: Harry Potter
        pages:
          type: integer
          example: 123