如何从SPARQL查询中获得SPARQL的问题答案？

Question

在下面的代码上执行的SPARQL的ASK查询在虚拟SPARQL查询编辑器上执行时返回true。同样的结果是我希望返回到我的脚本中。我如何调整sparqllib的使用？

<?php
    require_once('./sparqllib.php');
    $db = sparql_connect('http://dbpedia.org/sparql');

    $query = "
    ASK {
        ?book a dbpedia-owl:Book .
        ?book dbpprop:author ?author .
        ?book dbpprop:name ?bookname .
        ?author dbpprop:name ?authorname .
        FILTER regex(?bookname, 'A Tale of Two Cities', 'i') .
        FILTER regex(?authorname, 'Dickens', 'i')
    }";

    $result = sparql_query($query);
    var_dump($result);

var_dump()的结果：

object(sparql_result)[3]
  public 'rows' => 
    array (size=0)
      empty
  public 'fields' => 
    array (size=0)
      empty
  public 'db' => 
    object(sparql_connection)[1]
      public 'db' => null
      public 'debug' => boolean false
      public 'errno' => null
      public 'error' => null
      public 'ns' => 
        array (size=0)
          empty
      public 'params' => null
      public 'caps' => 
        array (size=0)
          empty
      public 'caps_desc' => 
        array (size=7)
          'select' => string 'Basic SELECT' (length=12)
          'constant_as' => string 'SELECT ("foo" AS ?bar)' (length=22)
          'math_as' => string 'SELECT (2+3 AS ?bar)' (length=20)
          'count' => string 'SELECT (COUNT(?a) AS ?n) ?b ... GROUP BY ?b' (length=43)
          'max' => string 'SELECT (MAX(?a) AS ?n) ?b ... GROUP BY ?b' (length=41)
          'sample' => string 'SELECT (SAMPLE(?a) AS ?n) ?b ... GROUP BY ?b' (length=44)
          'load' => string 'LOAD <...>' (length=10)
      public 'caps_cache' => null
      public 'caps_anysubject' => null
      public 'endpoint' => string 'http://dbpedia.org/sparql' (length=25)
  public 'i' => int 0

Answer 1

简短的回答(变通办法)

sparqllib.php似乎不支持处理ask查询的结果，因此您可能应该只使用

select * where {
    ?book a dbpedia-owl:Book .
    ?book dbpprop:author ?author .
    ?book dbpprop:name ?bookname .
    ?author dbpprop:name ?authorname .
    FILTER regex(?bookname, 'A Tale of Two Cities', 'i') .
    FILTER regex(?authorname, 'Dickens', 'i')
}
limit 1

看看你是否得到了结果。

长答案(sparqllib不支持ask结果)

我不认为sparqllib支持select查询以外的其他查询。如果您查看一下sparqllib.php，您可以看到查询是如何执行的：

function query( $query, $timeout=null )
{   
    $prefixes = "";
    foreach( $this->ns as $k=>$v )
    {
        $prefixes .= "PREFIX $k: <$v>\n";
    }
    $output = $this->dispatchQuery( $prefixes.$query, $timeout );
    if( $this->errno ) { return; }
    $parser = new xx_xml($output, 'contents');
    if( $parser->error() ) 
    { 
        $this->errno = -1; # to not clash with CURLOPT return; }
        $this->error = $parser->error();
        return;
    }
    return new sparql_result( $this, $parser->rows, $parser->fields );
}

dispatchQuery负责发送查询并返回结果。它在application/sparql-results+xml中请求它们，这就是为什么涉及到XML解析器的原因。如果您查看一下XML解析代码，会发现以下内容：

function startXML($parser, $name, $attr)    
{
    if( $name == "sparql" ) { $this->looks_legit = true; }
    if( $name == "result" )
    {
        $this->result = array();
    }
    if( $name == "binding" )
    {
        $this->part = $attr["name"];
    }
    if( $name == "uri" || $name == "bnode" )
    {
        $this->part_type = $name;
        $this->chars = "";
    }
    if( $name == "literal" )
    {
        $this->part_type = "literal";
        if( isset( $attr["datatype"] ) )
        {
            $this->part_datatype = $attr["datatype"];
        }
        if( isset( $attr["xml:lang"] ) )
        {
            $this->part_lang = $attr["xml:lang"];
        }
        $this->chars = "";
    }
    if( $name == "variable" )
    {
        $this->fields[] = $attr["name"];
    }
}

现在，如果您看一下SPARQL查询结果XML格式(第二版)，它定义了结果应该是什么样子，特别是2.3.2.布尔结果，我们就会看到询问查询的结果应该如下所示

sparqllib.php不包括任何东西来查找名为"boolean“的元素。它似乎只用于处理select结果。尽管如此，代码是在LGPL下授权的，并且根据文件头在GitHub上是可用的，所以如果您想要的话，您应该能够分叉它并添加ask支持：

###############################
# Christopher Gutteridge 2010
#  cjg@ecs.soton.ac.uk
#  LGPL License 
#  http://graphite.ecs.soton.ac.uk/sparqllib/
#  https://github.com/cgutteridge/PHP-SPARQL-Lib
###############################