Introspection does not work for Zefix

[BenjaminHofstetter]

https://spex.zazuko.com/#/?url=https://lindas.admin.ch/query&graph=https://lindas.admin.ch/foj/zefix&prefixes=admin:https://schema.ld.admin.ch/&forceIntrospection=false

This is a good example to investigate "Introspection" issues. Because the Schema is very simple.

Ontology

Classes

Just a small class count ...

SELECT ?class (count(?s) as ?count)
 FROM <https://lindas.admin.ch/foj/zefix>
 WHERE {
  ?s a ?class .
 } GROUP BY ?class order by ?count

	class	count
1	http://schema.org/DefinedTermSet	"1"^^xsd:integer
2	http://schema.org/Person	"1"^^xsd:integer
3	https://cube.link/meta/SharedDimension	"1"^^xsd:integer
4	http://www.w3.org/ns/dcat#Dataset	"1"^^xsd:integer
5	http://rdfs.org/ns/void#Dataset	"1"^^xsd:integer
6	http://schema.org/Dataset	"1"^^xsd:integer
7	http://www.w3.org/ns/locn#Address	"710619"^^xsd:integer
8	https://schema.ld.admin.ch/ZefixOrganisation	"710619"^^xsd:integer
9	http://schema.org/Organization	"710619"^^xsd:integer
10	http://schema.org/PostalAddress	"710619"^^xsd:integer
11	http://schema.org/DefinedTerm	"710619"^^xsd:integer
12	http://schema.org/PropertyValue	"2131857"^^xsd:integer

Predicates

SELECT ?p (COUNT(?s) AS ?count)
FROM <https://lindas.admin.ch/foj/zefix>
WHERE {
  {
    SELECT DISTINCT ?p WHERE {
    	?s ?p ?o.
    }
  }
  ?s ?p ?o .
} GROUP BY ?p ORDER BY DESC(?count)

	p	count
1	http://www.w3.org/1999/02/22-rdf-syntax-ns#type	"5684958"^^xsd:integer
2	http://schema.org/name	"2908101"^^xsd:integer
3	http://schema.org/identifier	"2131857"^^xsd:integer
4	http://schema.org/value	"2131857"^^xsd:integer
5	http://schema.org/address	"710619"^^xsd:integer
6	http://schema.org/streetAddress	"710619"^^xsd:integer
7	http://schema.org/inDefinedTermSet	"710619"^^xsd:integer
8	http://schema.org/addressRegion	"710619"^^xsd:integer
9	http://schema.org/addressLocality	"710619"^^xsd:integer
10	http://www.w3.org/ns/locn#postName	"710619"^^xsd:integer
11	https://schema.ld.admin.ch/municipality	"710619"^^xsd:integer
12	http://www.w3.org/ns/locn#adminUnitL2	"710619"^^xsd:integer
13	http://schema.org/legalName	"710619"^^xsd:integer
14	http://schema.org/additionalType	"710619"^^xsd:integer
15	http://www.w3.org/ns/locn#address	"710619"^^xsd:integer
16	http://www.w3.org/ns/locn#postCode	"706543"^^xsd:integer
17	http://schema.org/postalCode	"706543"^^xsd:integer
18	http://www.w3.org/ns/locn#thoroughfare	"703311"^^xsd:integer
19	http://schema.org/description	"700528"^^xsd:integer
20	http://www.w3.org/ns/locn#locatorDesignator	"689521"^^xsd:integer
21	http://www.w3.org/ns/locn#locatorName	"121365"^^xsd:integer
22	http://schema.org/areaServed	"35659"^^xsd:integer
23	http://www.w3.org/ns/locn#addressArea	"35659"^^xsd:integer
24	http://schema.org/postOfficeBoxNumber	"29362"^^xsd:integer
25	http://www.w3.org/ns/locn#poBox	"29362"^^xsd:integer
26	http://purl.org/dc/terms/keyword	"25"^^xsd:integer
27	http://purl.org/dc/terms/title	"4"^^xsd:integer
28	http://purl.org/dc/terms/description	"4"^^xsd:integer
29	http://purl.org/dc/terms/language	"4"^^xsd:integer
30	http://www.w3.org/ns/dcat#theme	"3"^^xsd:integer
31	http://schema.org/email	"2"^^xsd:integer
32	http://schema.org/datePublished	"1"^^xsd:integer
33	http://purl.org/dc/terms/identifier	"1"^^xsd:integer
34	http://schema.org/dateCreated	"1"^^xsd:integer
35	http://schema.org/dateModified	"1"^^xsd:integer
36	http://www.w3.org/ns/dcat#landingPage	"1"^^xsd:integer
37	http://purl.org/dc/terms/creator	"1"^^xsd:integer
38	http://www.w3.org/ns/dcat#contactPoint	"1"^^xsd:integer
39	http://purl.org/dc/terms/accrualPeriodicity	"1"^^xsd:integer
40	http://purl.org/dc/terms/coverage	"1"^^xsd:integer
41	http://purl.org/dc/terms/license	"1"^^xsd:integer
42	http://schema.org/publisher	"1"^^xsd:integer
43	http://www.w3.org/ns/dcat#accessURL	"1"^^xsd:integer
44	http://rdfs.org/ns/void#sparqlEndpoint	"1"^^xsd:integer
45	http://www.w3.org/ns/shacl#property	"1"^^xsd:integer
46	http://schema.org/dataset	"1"^^xsd:integer
47	http://purl.org/dc/terms/publisher	"1"^^xsd:integer
48	http://schema.org/familyName	"1"^^xsd:integer
49	http://schema.org/givenName	"1"^^xsd:integer
50	http://schema.org/creativeWorkStatus	"1"^^xsd:integer
51	http://rdfs.org/ns/void#exampleResource	"1"^^xsd:integer
52	http://qudt.org/schema/qudt/scaleType	"1"^^xsd:integer
53	http://schema.org/workExample	"1"^^xsd:integer
54	http://purl.org/dc/terms/issued	"1"^^xsd:integer
55	http://purl.org/dc/terms/modified	"1"^^xsd:integer
56	http://schema.org/validFrom	"1"^^xsd:integer
57	http://purl.org/dc/terms/rights	"1"^^xsd:integer

Introspection

The introspection query is like this ...

 SELECT DISTINCT ?cls ?property ?linktype ?datatype
      FROM <https://lindas.admin.ch/foj/zefix>
      WHERE {
        ?subject a ?cls .
        ?subject ?property ?object . # <--- this is a killer 

        OPTIONAL {
          ?object a ?linktype .
        }

        BIND(DATATYPE(?object) AS ?datatype)
      }

For this Zefix dataset the line "this is a killer" is a bit too much.