Adding certainty for "when" temporal element

[kgeographer]

Existing situation

Currently, geometry in Linked Places format (LPF) has a "certainty" attribute, which allows one of three values, "certain", "less-certain", and "uncertain" (see B below). This convention is the same as used in the Pleiades place model. Certainty was not included in the "when" object used to describe temporality, an oversight.

Note that the term "attribute" is synonymous with "property" and "relation." The "certainty" attribute can optionally apply to a single geometry element or to a geometry within a GeometryCollection.

It has been proposed to support the "certainty" attribute in the "when" element, wherever it is used, as illustrated in A. Note that it could be applied to any individual timespan or named period assertion.

Implications

Software that fully supports LPF will faithfully store, and/or render, and/or make available, entire records. It should do something to display each record's contents, including visually differentiating elements that have associated "certainty" attributes. Certainty is always optional so its absence should never cause validation to fail.

A. WHEN
1. Applying to entire when object

"when": {
  "timespans": [
    { "start": { "in": "yyyy-mm" },
      "end": {
          "earliest": "-yyyy",
          "latest": "yyyy-mm-dd" }
    }
  ],
  "periods": [
    { "name": "Anglo-Saxon Period, 449-1066",
      "uri": "http://n2t.net/ark:/99152/p06c6g3whtg" }
  ],
  "label": "for a century during the Anglo-Saxon period",
  "duration": "P100Y"
  "certainty": "less-certain"
}

2. Applying to any individual timespan or period

"when": {
  "timespans": [
    { "start": { "in": "yyyy-mm" },
      "end": {
          "earliest": "-yyyy",
          "latest": "yyyy-mm-dd" },
      "certainty": "less-certain"
    }
  ],
  "periods": [
    { "name": "Anglo-Saxon Period, 449-1066",
      "uri": "http://n2t.net/ark:/99152/p06c6g3whtg",
      "certainty": "certain"
    }
  ],
  "label": "for a century during the Anglo-Saxon period",
  "duration": "P100Y"
}

B. GEOMETRY
1. Single geometry

"geometry": { 
    "type": "Point",
    "coordinates": [-1.2879,51.6708],
    "geowkt": "POINT(-1.2879 51.6708)",
    "when": {"timespans":[
        {"start":{"earliest": "1600"},"end":{"in":"1699"}}
    ]},
    "certainty": "less-certain"
}

2. Geometry collection

"geometry": {
  "type": "GeometryCollection",
  "geometries": [
      { "type": "Point",
        "coordinates": [-1.2879,51.6708],
        "geowkt": "POINT(-1.2879 51.6708)",
        "when": {"timespans":[
            {"start":{"earliest": "1600"},"end":{"in":"1699"}}
        ]},
        "certainty": "less-certain"
      },
      { "geowkt": "POLYGON ((-1.3077 51.6542, -1.2555 51.6542,
            -1.2555 51.6908, -1.3077 51.6908, -1.3077 51.6542))",
        "when": {"timespans":[{"start":"1700"}]},
        "certainty": "certain"
      }
  ]
}