Licensing

  1. Machine-readable license
  2. Human-readable license
  3. License in the metadata

Machine-readable license

We can verify the presence of this type license in two ways:

  1. We look for it inside the VoID file, looking for the triple with the predicate dcterms: license.
  2. The other method involves executing query 4 on the SPARQL endpoints. The other method involves executing the following query on the SPARQL endpoints: 
    PREFIX cc: <http://creativecommons.org/ns#>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
PREFIX dct: <http://purl.org/dc/terms/>
PREFIX schema: <http://schema.org/>
PREFIX doap: <http://usefulinc.com/ns/doap#>
PREFIX xhtml: <http://www.w3.org/1999/xhtml#>
SELECT DISTINCT ?o
WHERE{
{?s ?p ?o}
VALUES (?p) {
(dct:license) (dct:rights)(cc:license)
(dc:license)(schema:license)(doap:license)
(xhtml:license)(dc:rights)
}
}

    Because queries with the VALUES function may not be supported from SPARQL endpoints that are based on SPARQL 1.0, alternative queries are provided which instead use the UNION. If a machine-readable license is indicated, we assign 1 to this metric, 0 otherwise.

Human-readable license

For this type of license we must access the triples of the KG to verify that there is a label understandable to the user on a triple. All the labels contained in the KG are recovered and then filtered using the following regex:

. ∗(licensed?|copyrighte?d?).∗(under|grante?d?|rights?)

The complete query that runs on the SPARQL endpoint is:

PREFIX rdf:<http://www.w3.org/2000/01/rdf-schema#>
PREFIX dct: <http://purl.org/dc/terms/>
PREFIX schema: <http://schema.org/>
SELECT ?o
WHERE{
{?s rdfs:label ?o}
UNION
{?s dct:description ?o}
UNION
{?s rdfs:comment ?o}
UNION
{?s rdfs:label ?o}
UNION
{?s schema:description ?o}
FILTER
regex(?o,
".*(licensed?|copyrighte?d?).*(under|grante?d?|rights?).*")
}

If a human-readable license is indicated, we assign 1 to this metric, 0 otherwise.

License in the metadata

In this case, we simply analyze the KG metadata and the value of the license key in it. If a license is indicated, we assign 1 to this metric, 0 otherwise.