And*_*rei 4 rdf sparql virtuoso
我正在尝试运行以下SPARQL查询,但它一直在返回SR171: Transaction timed out.
SELECT ?isBusAvailable WHERE {
SELECT DISTINCT IF (
(
SELECT ?value2 WHERE {
GRAPH data: { ?obsValueID2 ontology:value ?value2 }
GRAPH data: { ?obsValueID2 rdf:label "Availability" }
GRAPH data: { ?obsValueID2 ontology:isObservedValueOf ?obsID2}
GRAPH data: { ?obsID2 ssn:observationResultTime ?time2 }
GRAPH data: { ?obsID2 ssn:observedBy ?id2 }
GRAPH meta: { ?id2 rdf:label "MyBusService" }
} ORDER BY DESC (?time2) LIMIT 1) > 1, "Take Bus", (
SELECT ?isBikeAvailable WHERE {
SELECT DISTINCT IF (
(
SELECT ?value3 WHERE {
GRAPH data: { ?obsValueID3 ontology:value ?value3 }
GRAPH data: { ?obsValueID3 rdf:label "Availability" }
GRAPH data: { ?obsValueID3 ontology:isObservedValueOf ?obsID3}
GRAPH data: { ?obsID3 ssn:observationResultTime ?time3 }
GRAPH data: { ?obsID3 ssn:observedBy ?id3 }
GRAPH meta: { ?id3 rdf:label "MyBikeService" }
} ORDER BY DESC (?time3) LIMIT 1
) > 0, "Take Bike", "Take Taxi") as ?isBikeAvailable WHERE { ?1 ?2 ?3}})) as ?isBusAvailable WHERE { ?4 ?5 ?6}}
如果我单独运行它,它会在1秒内运行.以下示例有效.
SELECT ?isBusAvailable WHERE {
SELECT DISTINCT IF (
(
SELECT ?value2 WHERE {
GRAPH data: { ?obsValueID2 ontology:value ?value2 }
GRAPH data: { ?obsValueID2 rdf:label "Availability" }
GRAPH data: { ?obsValueID2 ontology:isObservedValueOf ?obsID2}
GRAPH data: { ?obsID2 ssn:observationResultTime ?time2 }
GRAPH data: { ?obsID2 ssn:observedBy ?id2 }
GRAPH meta: { ?id2 rdf:label "MyBusService" }
} ORDER BY DESC (?time2) LIMIT 1) > 1, "Take Bus", 'Take Bike') as ?isBusAvailable WHERE { ?4 ?5 ?6}}
如果第一个查询的结果为true,则返回'Take Bus'; 否则,运行第二个查询,然后返回'Take Bike'或'Take Taxi'.
显然问题在于第二个查询(来自第一个查询的错误条件).在"Take Bus"之后,如果我将第二个查询更改为"Take Bike",它就可以了.
@andrei - 我认为你的?isBusAvailable困惑很重要 - 考虑到你最后返回的文字值,这可能会更好?travelMethod.
在我阅读内容时,这里的问题实际上是如何正确构建嵌套IFs- 问题的标题应该是"在SPARQL中嵌套IF语句的正确语法是什么？"
在简单的流程中,我认为您正在做的是检查可用的公共汽车,并返回"乘坐公共汽车",如果存在的话; 如果没有,你检查一辆可用的自行车,并返回"骑自行车",如果存在的话; 如果没有,你返回"乘坐出租车".在伪代码中IF AVAIL bus, THEN take bus, ELSE ( IF AVAIL bike, THEN take bike, ELSE take taxi ).
@ joshua-taylor关于一件事是正确的 - SELECT DISTINCT IF (…)不是严格有效,但修复只是一个额外的paren包装 - 例如,以下是有效的(和验证) -
SELECT DISTINCT ( IF ( ( 1 = 1 )
, "true"
, "false"
) AS ?test )
WHERE { ?x ?y ?z }
LIMIT 1
但是在查询中修复此问题并不会从验证程序获得更好的输出.实际上,替换内部(SELECT ?value … LIMIT 1)查询1会使整个大型查询生效 -
SELECT ?travelMethod
WHERE
{
SELECT DISTINCT
( IF
(
(
1 > 0
)
, "Take Bus"
, (
IF (
(
1 > 0
)
, "Take Bike"
, "Take Taxi"
)
)
) AS ?travelMethod
)
FROM data:
WHERE { ?1 ?2 ?3 }
}
- 这些内部(SELECT ?value … LIMIT 1)查询也会自行验证 -
SELECT ?value
WHERE
{
GRAPH data: { ?obsValueID ontology:value ?value }
GRAPH data: { ?obsValueID rdf:label "Availability" }
GRAPH data: { ?obsValueID ontology:isObservedValueOf ?obsID }
GRAPH data: { ?obsID ssn:observationResultTime ?time }
GRAPH data: { ?obsID ssn:observedBy ?id }
GRAPH meta: { ?id rdf:label "MyBusService" }
}
ORDER BY DESC (?time)
LIMIT 1
我相信以下是有效的语法 - 即使sparql.org验证器扼杀它 - 但我不能确定它执行,因为我没有时间重新调整查询以针对随机端点和数据集运行.如果您重新编写查询以运行DBpedia,那么您可以帮助下一个人!
SELECT ?travelMethod
WHERE
{
SELECT DISTINCT
( IF
(
(
( SELECT ?value
WHERE
{
GRAPH data: { ?obsValueID ontology:value ?value }
GRAPH data: { ?obsValueID rdf:label "Availability" }
GRAPH data: { ?obsValueID ontology:isObservedValueOf ?obsID }
GRAPH data: { ?obsID ssn:observationResultTime ?time }
GRAPH data: { ?obsID ssn:observedBy ?id }
GRAPH meta: { ?id rdf:label "MyBusService" }
}
ORDER BY DESC (?time)
LIMIT 1
) > 0
)
, "Take Bus"
, (
IF (
(
( SELECT ?value
WHERE
{
GRAPH data: { ?obsValueID ontology:value ?value }
GRAPH data: { ?obsValueID rdf:label "Availability" }
GRAPH data: { ?obsValueID ontology:isObservedValueOf ?obsID }
GRAPH data: { ?obsID ssn:observationResultTime ?time }
GRAPH data: { ?obsID ssn:observedBy ?id }
GRAPH meta: { ?id rdf:label "MyBikeService" }
}
ORDER BY DESC (?time)
LIMIT 1
) > 0
)
, "Take Bike"
, "Take Taxi"
)
)
) AS ?travelMethod
)
FROM data:
WHERE { ?1 ?2 ?3 }
}
花了一点时间远离它,并在上面的评论中重新阅读你对数据所说的内容,我可以进一步优化这个查询,这也可以使它更快地执行 -
SELECT ?travelMethod
WHERE
{
SELECT DISTINCT
( IF
(
(
( SELECT ?value
WHERE
{
GRAPH data: { ?obsValueID ontology:value ?value
; rdf:label "Availability"
; ontology:isObservedValueOf ?obsID
. ?obsID ssn:observationResultTime ?time
; ssn:observedBy ?id
}
GRAPH meta: { ?id rdf:label "MyBusService" }
}
ORDER BY DESC (?time)
LIMIT 1
) > 0
)
, "Take Bus"
, (
IF (
(
( SELECT ?value
WHERE
{
GRAPH data: { ?obsValueID ontology:value ?value
; rdf:label "Availability"
; ontology:isObservedValueOf ?obsID
. ?obsID ssn:observationResultTime ?time
; ssn:observedBy ?id
}
GRAPH meta: { ?id rdf:label "MyBikeService" }
}
ORDER BY DESC (?time)
LIMIT 1
) > 0
)
, "Take Bike"
, "Take Taxi"
)
)
) AS ?travelMethod
)
FROM data:
WHERE { ?1 ?2 ?3 }
}
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