{
  "@context": {
    "ex": "http://example.org/vocab#",
    "ex:contains": {"@type": "@id"}
  },
  "@graph": [
    {
      "@id": "http://example.org/test/#library",
      "@type": "ex:Library",
      "ex:contains": "http://example.org/test#book"
    },
    {
      "@id": "http://example.org/test#book"
    }
  ]
}