timeline.json

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "width": 600,
  "height": 200,
  "data":[
    { "name": "visualization_libraries",
      "format": {
            "type": "json",
            "parse": {
              "release": "date:'%Y'"
            }
      },
      "values": [
        {"name":"vega", "release":"2013"},
        {"name":"d3","release":"2011"}, 
        {"name":"plotly","release":"2012"}
        ]
    }
  ],
  "scales": [
    {
      "name": "x_scale",
      "type": "time",
      "domain": {"data": "visualization_libraries","field": "release"},
      "range": [0, 600],
      "nice": "year"
    }
  ],
  "marks":[
    {
      "type": "rect",
      "name": "rectangles",
      "from": {"data": "visualization_libraries"},
      "encode": {
        "enter": {
          "width": {"value": 60},
          "height": {"value": 20},
          "x": {
            "signal": "scale('x_scale', datum.release)"
          },
          "y": {"value": 10}
        }
      }  
    },
    {
      "type": "text",
      "name": "labels",
      "from": {"data": "rectangles"},
      "encode": {
        "enter": {
          "text": {"signal": "datum.datum.name"},
          "x": {
            "signal": "datum.x+30"
          },
          "y": {"value": 20},
          "align": {"value": "center"},
          "baseline": {"value": "middle"},
          "fontWeight": {"value": "bold"},
          "fill": {"value": "black"}
        }
      }
    },
    {
      "type": "rule",
      "name": "lines",
      "from": {"data": "labels"},
      "encode": {
        "enter": {
          "x": {"signal": "datum.x"},
          "x2": {"signal": "datum.x"},
          "y": {"signal": "datum.y+10"},
          "y2": {"signal": "height"}
        }
      }
    }
  ],
  "axes":[
    {
      "scale": "x_scale",
      "orient": "bottom",
      "format": "%b/%Y"
    }
  ]
}