Re: [dxwg] should DCAT 3 provide its own way to indicate the query to pose to the data service endpoints? (#1230)

looking at https://www.w3.org/TR/vocab-dcat-2/#dcat-scope diagram:
a dcat:Distribution can have a dcat:dataService link to a dcat:DataService.  I think dcat:DataService is analogous to schema.org (sdo) WebAPI.  To describe the API requires a variety of information. Proposal in Schema.org is to use [sdo:potentialAction/sdo:Action](https://schema.org/potentialAction) (which has various sub classes for different actions; important to look at [Actions Overview](http://schema.org/docs/actions.html) ).  These would need to be implemented in dcat:DataService.

Here is some [example code](https://github.com/earthcubearchitecture-ecresourcereg/infomodel/blob/4b7cdaf408522d03edc0f096708103cc17a451e7/examples/Service-IRIS-fsdnEvent-JSON.json) (follows suggestions in [schemaorg/schemaorg#2342](https://github.com/schemaorg/schemaorg/issues/2342 ); base namespace is sdo):

```
"potentialAction": [
  {
    "@type": "SearchAction",
    "name": "Query",
    "description": "query service to obtain records of seismic events",
    "result":
        {
	"@type": "DataDownload",
	"encodingFormat": ["application/xml+QuakeML",	"text/csv","QuakeML", "text/csv+geocsv",	"GeoCSV-SeismicEvent"	],
	"description": "XML, csv, or csv fromat for seismic event following EarthCube geoWs conventions."
	},
    "target": {
	"@type": "EntryPoint",
	"urlTemplate": "http://service.iris.edu/fdsnws/event/1/query?{geographic-constraints}&{depth-constraints}&{temporal-constraints}&{magnitude-constraints}&{organization-constraints}&{misc-parameters}&{format-option}&{nodata=404}",
	"description": "URL with multiple query paramters--geographic location, event depth, time period of event, event magnitude, source network, miscellaneous parameters, formt for returned data, and what flat to use for no data.  TBD-- how to handle POST request version; need to specify the format for the POST content",
	"httpMethod":"GET",
	"uriTemplate-input": [
		{
		"@id": "urn:iris:fsdn.starttime",
		"@type": "PropertyValueSpecification",
		"valueName": "start",
		"defaultValue": "Any",
		"description": "allowed: Any valid time. Limit to events on or after the specified start time; use UTC for time zone",
		"valueRequired": true,
		"valuePattern": "(-?(?:[1-9][0-9]*)?[0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])(.[0-9]+)?",
		"xsd:type": "dateTime"
		},
		{
		"@id": "urn:iris:fsdn.endtime",
		"@type": "PropertyValueSpecification",
		"valueName": "end",
		"defaultValue": "Any",
		"description": "allowed: Any valid time. Limit to events on or before the specified start time",
		"valueRequired": true,
		"valuePattern": "(-?(?:[1-9][0-9]*)?[0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])(.[0-9]+)?"
		},

```
 not all parameters shown. Parameters in the template are enclosed in braces ('{}'). See [IETF RFC-6570](https://tools.ietf.org/html/rfc6570)

```
]
	},
  "object": {
	"@type": "DataFeed",
	"description": "list of properties  that are included in seismic event description in response documents",
	"variableMeasured": [
		{
			"@type": "PropertyValue",
			"name": "name of the variable",
			"description": "example of documentation for a varible provided in the result object",
			"propertyID": "URI for the property in some ontology",
			"measurementTechnique": "URI for the measurement protocol, or text description of procedure and sensor"
		} ,
...
```
... more variables in response...
close
```
	]	
} }
```

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