{
  "type": "project",
  "input": {
    "type": "leftjoin",
    "input": [
      {
        "type": "service",
        "input": {
          "type": "bgp",
          "patterns": [
            {
              "type": "pattern",
              "termType": "Quad",
              "subject": {
                "termType": "Variable",
                "value": "s"
              },
              "predicate": {
                "termType": "Variable",
                "value": "p"
              },
              "object": {
                "termType": "Variable",
                "value": "o1"
              },
              "graph": {
                "termType": "DefaultGraph",
                "value": ""
              }
            }
          ]
        },
        "name": {
          "termType": "NamedNode",
          "value": "http://example1.org/sparql"
        },
        "silent": false
      },
      {
        "type": "service",
        "input": {
          "type": "bgp",
          "patterns": [
            {
              "type": "pattern",
              "termType": "Quad",
              "subject": {
                "termType": "Variable",
                "value": "s"
              },
              "predicate": {
                "termType": "Variable",
                "value": "p2"
              },
              "object": {
                "termType": "Variable",
                "value": "o2"
              },
              "graph": {
                "termType": "DefaultGraph",
                "value": ""
              }
            }
          ]
        },
        "name": {
          "termType": "NamedNode",
          "value": "http://example2.org/sparql"
        },
        "silent": false
      }
    ]
  },
  "variables": [
    {
      "termType": "Variable",
      "value": "s"
    },
    {
      "termType": "Variable",
      "value": "o1"
    },
    {
      "termType": "Variable",
      "value": "o2"
    }
  ]
}