SPARQL 我们什么时候使用 "a"
SPARQL When do we use the "a"
我是 SPARQL 的新手。我阅读了关于 Jena (https://jena.apache.org/tutorials/sparql.html) 的教程并且我理解了大部分示例。但是我真的不明白什么时候我们必须使用 a
例如这个三元组:
@prefix vCard: <http://www.w3.org/2001/vcard-rdf/3.0#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
<http://somewhere/MattJones/> vCard:FN "Matt Jones" .
<http://somewhere/MattJones/> vCard:N _:b0 .
_:b0 vCard:Family "Jones" .
_:b0 vCard:Given "Matthew" .
<http://somewhere/RebeccaSmith/> vCard:FN "Becky Smith" .
<http://somewhere/RebeccaSmith/> vCard:N _:b1 .
_:b1 vCard:Family "Smith" .
_:b1 vCard:Given "Rebecca" .
<http://somewhere/JohnSmith/> vCard:FN "John Smith" .
<http://somewhere/JohnSmith/> vCard:N _:b2 .
_:b2 vCard:Family "Smith" .
_:b2 vCard:Given "John" .
<http://somewhere/SarahJones/> vCard:FN "Sarah Jones" .
<http://somewhere/SarahJones/> vCard:N _:b3 .
_:b3 vCard:Family "Jones" .
_:b3 vCard:Given "Sarah" .
我们可以这样写:
PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>
SELECT ?y ?givenName
WHERE
{ ?y vcard:Family "Smith" .
?y vcard:Given ?givenName .
}
但是我在课程的幻灯片中发现了这样的东西:
SELECT ?label_du_président ?âge_du_président ? label_du_pays
WHERE {
?une_élection a ex:electionPrésidentielle .
?une_élection ex:gagnéePar ?un_president .
?une_élection ex:alieuDans ?un_pays .
?un_president rdfs:label ?label_du_president .
?un_president ex:âge ?âge_du_president .
?un_pays rdfs:label ?label_du_pays
}
为什么以及何时使用 a
?
它是 rdf:type
属性 的 shorthand 符号。来自 SPARQL Query Language specs:
The keyword "a" can be used as a predicate in a triple pattern and is an alternative for the IRI http://www.w3.org/1999/02/22-rdf-syntax-ns#type. This keyword is case-sensitive.
将其视为意义 "is a (kind of)"。
我是 SPARQL 的新手。我阅读了关于 Jena (https://jena.apache.org/tutorials/sparql.html) 的教程并且我理解了大部分示例。但是我真的不明白什么时候我们必须使用 a
例如这个三元组:
@prefix vCard: <http://www.w3.org/2001/vcard-rdf/3.0#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
<http://somewhere/MattJones/> vCard:FN "Matt Jones" .
<http://somewhere/MattJones/> vCard:N _:b0 .
_:b0 vCard:Family "Jones" .
_:b0 vCard:Given "Matthew" .
<http://somewhere/RebeccaSmith/> vCard:FN "Becky Smith" .
<http://somewhere/RebeccaSmith/> vCard:N _:b1 .
_:b1 vCard:Family "Smith" .
_:b1 vCard:Given "Rebecca" .
<http://somewhere/JohnSmith/> vCard:FN "John Smith" .
<http://somewhere/JohnSmith/> vCard:N _:b2 .
_:b2 vCard:Family "Smith" .
_:b2 vCard:Given "John" .
<http://somewhere/SarahJones/> vCard:FN "Sarah Jones" .
<http://somewhere/SarahJones/> vCard:N _:b3 .
_:b3 vCard:Family "Jones" .
_:b3 vCard:Given "Sarah" .
我们可以这样写:
PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>
SELECT ?y ?givenName
WHERE
{ ?y vcard:Family "Smith" .
?y vcard:Given ?givenName .
}
但是我在课程的幻灯片中发现了这样的东西:
SELECT ?label_du_président ?âge_du_président ? label_du_pays
WHERE {
?une_élection a ex:electionPrésidentielle .
?une_élection ex:gagnéePar ?un_president .
?une_élection ex:alieuDans ?un_pays .
?un_president rdfs:label ?label_du_president .
?un_president ex:âge ?âge_du_president .
?un_pays rdfs:label ?label_du_pays
}
为什么以及何时使用 a
?
它是 rdf:type
属性 的 shorthand 符号。来自 SPARQL Query Language specs:
The keyword "a" can be used as a predicate in a triple pattern and is an alternative for the IRI http://www.w3.org/1999/02/22-rdf-syntax-ns#type. This keyword is case-sensitive.
将其视为意义 "is a (kind of)"。