java - 耶拿 ARQ 中子选择的绑定(bind)值存在问题

Question

我想运行以下简单的测试查询:

PREFIX  rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX  vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>

SELECT  ?givenName ?name_count ?temp
WHERE
  { BIND(if(( ?name_count = 2 ), "just two", "definitely not 2") AS ?temp)
    { SELECT DISTINCT  ?givenName (COUNT(?givenName) AS ?name_count)
      WHERE
        { ?y  vcard:Family  ?givenName }
      GROUP BY ?givenName
    }
  }

我正在查询的图表来自教程 https://jena.apache.org/tutorials/sparql_data.html :

@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" .

现在的问题是用 Jena 运行它:

Query query = QueryFactory.create(theAboveQueryAsString);
QueryExecution qexec = QueryExecutionFactory.create(query, theAboveGraphmodel);
ResultSet execSel = qexec.execSelect();
ResultSetRewindable results = ResultSetFactory.copyResults(execSel);;
ResultSetFormatter.out(System.out, results, query);

在控制台中给出这个结果:

----------------------------------
| givenName | name_count | temp  |
==================================
| "Smith"   | 2          |       |
| "Jones"   | 2          |       |
----------------------------------

将临时值设置为 null。

另一方面，在 Ontotext GraphDb 环境中的同一个图表上运行相同的查询，我得到了正确的结果(保存为 CSV):

givenName  |  name_count  |  temp
------------------------------------
Jones      |       2      |  just two
Smith      |       2      |  just two

ARQ 引擎中是否存在错误，或者我是否遗漏了某些内容？提前致谢。

我正在使用 jena-arq 3.12.0Java(TM) SE 运行时环境(版本 1.8.0_181-b13)Eclipse版本版本:2019-06(4.12.0)

Answer 1

BIND 和子选择之间有一个连接。连接步骤的参数是在连接完成之前计算的。因此，对 BIND 进行求值，对子选择进行单独求值，然后将结果连接起来。 BIND 分配中未设置 ?name_count。如果将其移到子选择之后，它将应用于子选择的结果。

BIND 将绑定(bind)添加到之前模式的结果。

(base <http://example/base/>
  (prefix ((rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>)
           (vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>))
    (project (?givenName ?name_count ?temp)
      (join
        (extend ((?temp (if (= ?name_count 2) "just two" "definitely not 2")))
          (table unit))
        (distinct
          (project (?givenName ?name_count)
           (extend ((?name_count ?.0))
             (group (?givenName) ((?.0 (count ?givenName)))
               (bgp (triple ?y vcard:Family ?givenName))))))))))

这里，(extend...) 是 (join...) 的两个参数之一。 (表单元) 是 BIND 之前的“无”。

如果放在后面，代数为:

(base <http://example/base/>
  (prefix ((rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>)
           (vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>))
    (project (?givenName ?name_count ?temp)
      (extend ((?temp (if (= ?name_count 2) "just two" "definitely not 2")))
        (distinct
          (project (?givenName ?name_count)
            (extend ((?name_count ?.0))
              (group (?givenName) ((?.0 (count ?givenName)))
                (bgp (triple ?y vcard:Family ?givenName))))))))))

并且extend(来自语法BIND)正在处理子查询的(distinct ...。