Wikibase EDTF

RDF export

Wikibase EDTF gives its value to the native RDF export mechanism using the datatypes xsd:EDTF datatype (e.g. "1867-05-26"^^xsd:edtf) and xsd:dateTime. For the latter datatype it turns EDTF values into standard Wikibase time (xsd:dateTime) values. Because Wikibase time values are a lot less expressive, the EDTF values are simplified in this process:

• EDTF date or time: Precision and time zone are retained. Qualifications and unspecified digits are discarded.
• EDTF Set: Each date in the set is exported.
• EDTF Season: One date for each month is exported, each having month precision.
• EDTF Interval: Nothing is exported (since there does not seem to be a reasonable default).

For cases where multiple dates are put in the RDF export, like with seasons and sets, there is nothing in the RDF indicating these values logically belong together.

If you can read PHP, you can see the simplification code in TimeValueBuilder.php.

Apparent duplicate results using SPARQL / Blazegraph

Because EDTF exposes the values as both xsd:edtf and a dumbed down xsd:dateTime you will get two values when querying properties with this datatype. using a filter in your SPARQL query can remove the value that you are not interested in:

#shows only the raw EDTF string from the query results, in this case ?date
FILTER ( datatype(?date) = xsd:edtf )

#shows only the dumbed down EDTF strings from the query results, in this case ?date
FILTER ( datatype(?date) = xsd:dateTime )

Note that if you are using OPTIONAL on the property, then you need to move the FILTER within the OPTIONAL statement.