A period of time can just have an end date

[andrea-perego]

Currently, the cardinality of these properties is defined as follows:

1 to 1, for dcat:startDate:

dcat-ep/0.3/dcat-ep.shacl.ttl

Lines 1499 to 1509 in 2f920e9

	epsh:P116 a skos:Concept;
	owl:versionInfo "v0.2";
	skos:inScheme <https://data.europarl.europa.eu/def/dcat-ep#>;
	skos:topConceptOf <https://data.europarl.europa.eu/def/dcat-ep#>;
	sh:datatype xsd:dateTime;
	sh:description "This property contains the start of the period.";
	sh:maxCount 1;
	sh:minCount 1;
	sh:name "start date"@en;
	sh:nodeKind sh:Literal;
	sh:path dcat:startDate .

0 to 1, for dcat:endDate:

dcat-ep/0.3/dcat-ep.shacl.ttl

Lines 1511 to 1520 in 2f920e9

	epsh:P117 a skos:Concept;
	owl:versionInfo "v0.2";
	skos:inScheme <https://data.europarl.europa.eu/def/dcat-ep#>;
	skos:topConceptOf <https://data.europarl.europa.eu/def/dcat-ep#>;
	sh:datatype xsd:dateTime;
	sh:description "This property contains the end of the period.";
	sh:maxCount 1;
	sh:name "end date"@en;
	sh:nodeKind sh:Literal;
	sh:path dcat:endDate .

This implies that a time interval can be open-ended - i.e., a time interval can have only the start date.

However, the usage note of dcterms:PeriodOfTime in DCAT allows also for time intervals having only the end date - quoting from §6.15 Class: Period of Time:

The start and end of the interval SHOULD be given by using properties dcat:startDate or time:hasBeginning, and dcat:endDate or time:hasEnd, respectively. The interval can also be open - i.e., it can have just a start or just an end.

To comply with this, the following revisions are needed:

• The min cardinality of dcat:startDate should be set to 0
• The fact that dcterms:PeriodOfTime must have at least a start or end date can be specified by using a sh:or constraint on these two properties