带圆括号的 sparql 查询抛出异常

Question

我正在尝试为某些人从 DBpedia 中提取标签。我现在部分成功，但我陷入了以下问题。以下代码有效。

public class DbPediaQueryExtractor {
    public static void main(String [] args) {
        String entity = "Aharon_Barak";
        String queryString ="PREFIX dbres: <http://dbpedia.org/resource/> SELECT * WHERE {dbres:"+ entity+ "<http://www.w3.org/2000/01/rdf-schema#label> ?o FILTER (langMatches(lang(?o),\"en\"))}";
        //String queryString="select *     where { ?instance <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person>;  <http://www.w3.org/2000/01/rdf-schema#label>  ?o FILTER (langMatches(lang(?o),\"en\"))  } LIMIT 5000000";
        QueryExecution qexec = getResult(queryString);
        try {
            ResultSet results = qexec.execSelect();
            for ( ; results.hasNext(); )
            {
                QuerySolution soln = results.nextSolution();
                System.out.print(soln.get("?o") + "\n");
            }
        }
        finally {
            qexec.close();
        }
    }

    public static QueryExecution getResult(String queryString){
        Query query = QueryFactory.create(queryString);
        //VirtuosoQueryExecution vqe = VirtuosoQueryExecutionFactory.create (sparql, graph);
        QueryExecution qexec = QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql", query);
        return qexec;
    }
}

但是，当实体包含括号时，它不起作用。例如，

String entity = "William_H._Miller_(writer)";

导致此异常:

Exception in thread "main" com.hp.hpl.jena.query.QueryParseException: Encountered " "(" "( "" at line 1, column 86.`

问题是什么？

Answer 1

它需要一些复制和粘贴才能看到到底发生了什么。我建议您在查询中添加换行符以便于阅读。您正在使用的查询是:

PREFIX dbres: <http://dbpedia.org/resource/>
SELECT * WHERE
{
  dbres:??? <http://www.w3.org/2000/01/rdf-schema#label> ?o 
  FILTER (langMatches(lang(?o),"en"))
}

其中 ??? 被字符串 entity 的内容替换。您在这里绝对没有进行输入验证，以确保 entity 的值可以合法粘贴。根据您的问题，听起来 entity 包含 William_H._Miller_(writer) ，所以您得到了查询:

PREFIX dbres: <http://dbpedia.org/resource/>
SELECT * WHERE
{
  dbres:William_H._Miller_(writer) <http://www.w3.org/2000/01/rdf-schema#label> ?o 
  FILTER (langMatches(lang(?o),"en"))
}

您可以将其粘贴到 public DBpedia endpoint 中，您将收到类似的解析错误消息:

Virtuoso 37000 Error SP030: SPARQL compiler, line 6: syntax error at 'writer' before ')'

SPARQL query:
define sql:big-data-const 0 
#output-format:text/html
define sql:signal-void-variables 1 define input:default-graph-uri <http://dbpedia.org> PREFIX dbres: <http://dbpedia.org/resource/>
SELECT * WHERE
{
  dbres:William_H._Miller_(writer) <http://www.w3.org/2000/01/rdf-schema#label> ?o 
  FILTER (langMatches(lang(?o),"en"))
}

比使用错误查询命中 DBpedia 的端点更好，您还可以使用 the SPARQL query validator 报告该查询:

Syntax error: Lexical error at line 4, column 34. Encountered: ")" (41), after : "writer"

在 Jena 中，您可以使用 ParameterizedSparqlString 来避免此类问题。这是您的示例，经过重新设计以使用参数化字符串:

import com.hp.hpl.jena.query.ParameterizedSparqlString;

public class PSSExample {
    public static void main( String[] args ) {
        // Create a parameterized SPARQL string for the particular query, and add the 
        // dbres prefix to it, for later use.
        final ParameterizedSparqlString queryString = new ParameterizedSparqlString(
                "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>\n" +
                "SELECT * WHERE\n" +
                "{\n" +
                "  ?entity rdfs:label ?o\n" +
                "  FILTER (langMatches(lang(?o),\"en\"))\n" +
                "}\n"
                ) {{
            setNsPrefix( "dbres", "http://dbpedia.org/resource/" );
        }};

        // Entity is the same. 
        final String entity = "William_H._Miller_(writer)";

        // Now retrieve the URI for dbres, concatentate it with entity, and use
        // it as the value of ?entity in the query.
        queryString.setIri( "?entity", queryString.getNsPrefixURI( "dbres" )+entity );

        // Show the query.
        System.out.println( queryString.toString() );
    }
}

输出是:

PREFIX dbres: <http://dbpedia.org/resource/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT * WHERE
{
  <http://dbpedia.org/resource/William_H._Miller_(writer)> rdfs:label ?o
  FILTER (langMatches(lang(?o),"en"))
}

您可以在公共(public)端点运行此查询并获取 the expected results 。请注意，如果您使用不需要特殊转义的 entity，例如，

final String entity = "George_Washington";

那么查询输出将使用前缀形式:

PREFIX dbres: <http://dbpedia.org/resource/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT * WHERE
{
  dbres:George_Washington rdfs:label ?o
  FILTER (langMatches(lang(?o),"en"))
}

这非常方便，因为您不必检查您的后缀，即 entity 是否有任何需要转义的字符； Jena 会为您解决这些问题。