Java Jena sparql(Dbpedia)查询可选筛选器不提供结果,但(http://dbpedia.org/snorql/)同样的查询工作
您好,我正在这个网站上进行此查询 但在我的jena queryFactory java类中,只有在以下行中删除缩略图的可选过滤器时,它才起作用:Java Jena sparql(Dbpedia)查询可选筛选器不提供结果,但(http://dbpedia.org/snorql/)同样的查询工作,java,sparql,jena,dbpedia,Java,Sparql,Jena,Dbpedia,您好,我正在这个网站上进行此查询 但在我的jena queryFactory java类中,只有在以下行中删除缩略图的可选过滤器时,它才起作用: OPTIONAL {?author <http://dbpedia.org/ontology/thumbnail> ?thumb }. "<http://dbpedia.org/ontology/thumbnail> ?thumb.\n" + 下面是我的jena java方法: private String authorQu
OPTIONAL {?author <http://dbpedia.org/ontology/thumbnail> ?thumb }.
"<http://dbpedia.org/ontology/thumbnail> ?thumb.\n" +
下面是我的jena java方法:
private String authorQuery(String entity, String keyWord, String language) {
return addPrefix("rdfs: <http://www.w3.org/2000/01/rdf-schema#>") +
addPrefix("rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>") +
addPrefix("dbpprop: <http://dbpedia.org/property/>") +
addPrefix("ontology: <http://dbpedia.org/ontology/>") +
addQuery("SELECT DISTINCT ?author ?name ?wiki ?desc ?thumb WHERE {\n" +
"?author a ontology:" + entity + ";\n" +
"rdfs:label ?name;\n" +
"ontology:wikiPageID ?wiki;\n" +
"ontology:abstract ?desc;\n" +
"<http://dbpedia.org/ontology/thumbnail> ?thumb.\n" +
"FILTER (lang(?name) = '" + language + "') " +
"FILTER (regex(?name, \"" + keyWord + "\") || regex(?desc, \"" + keyWord + "\"))\n" +
" FILTER (lang(?desc) = '" + language + "')." +
"}\n" +
"ORDER BY ?name\n" +
"LIMIT 40000");
}
但只要我在这行中添加optionnal关键字:
OPTIONAL {?author <http://dbpedia.org/ontology/thumbnail> ?thumb }.
"<http://dbpedia.org/ontology/thumbnail> ?thumb.\n" +
没有返回结果,有人能告诉我原因吗
PS:它在没有可选过滤器的情况下运行良好
编辑:整个DbpediaQuery类
public class DbPediaQuery {
//array of authors
private DbPediaQuery() {
}
public static DbPediaQuery createDbPediaQuery() {
return new DbPediaQuery();
}
public LinkedList<Entity> queryAuthor(String entity, String keyWord, String language) {
LinkedList<Entity> temp = new LinkedList<>();
Query query = QueryFactory.create(authorQuery(entity, keyWord, language));
QueryExecution qexec = QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql", query);
try {
temp.addAll(collectAuthors(qexec.execSelect()));
} catch (Exception e) {
e.printStackTrace();
}
return temp;
}
private String authorQuery(String entity, String keyWord, String language) {
return addPrefix("rdfs: <http://www.w3.org/2000/01/rdf-schema#>") +
addPrefix("rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>") +
addPrefix("dbpprop: <http://dbpedia.org/property/>") +
addPrefix("ontology: <http://dbpedia.org/ontology/>") +
addQuery("SELECT DISTINCT ?author ?name ?wiki ?desc ?thumb WHERE {\n" +
"?author a ontology:" + entity + ";\n" +
"rdfs:label ?name;\n" +
"ontology:wikiPageID ?wiki;\n" +
"ontology:abstract ?desc;\n" +
"<http://dbpedia.org/ontology/thumbnail> ?thumb.\n" +
"FILTER (lang(?name) = '" + language + "') " +
"FILTER (regex(?name, \"" + keyWord + "\") || regex(?desc, \"" + keyWord + "\"))\n" +
" FILTER (lang(?desc) = '" + language + "')." +
"}\n" +
"ORDER BY ?name\n" +
"LIMIT 40000");
}
private LinkedList<Entity> collectAuthors(ResultSet results) {
LinkedList<Entity> temp = new LinkedList<>();
while (results.hasNext()) {
Entity a = new Entity();
QuerySolution row = results.next();
String fullName = row.get("name").toString().substring(0, row.get("name").toString().indexOf("@"));
String biography = row.get("desc").toString().substring(0, row.get("desc").toString().indexOf("@"));
a.setTitle(fullName);
a.setWikiID(Integer.parseInt(row.get("wiki").toString().substring(0, row.get("wiki").toString().indexOf("^"))));
if (!row.get("thumb").toString().isEmpty())
a.setPictureURL(row.get("thumb").toString());
else
a.setPictureURL("http://www.google.fr/imgres?imgurl=http%3A%2F%2Fwww.elated.com%2Fres%2FImage%2Farticles%2Fmanagement%2Fapache%2Fmaking-a-custom-error-page%2Fapache_404_default.gif&imgrefurl=https%3A%2F%2Fgithub.com%2Fjdorn%2Fphp-reports%2Fissues%2F43&h=241&w=400&tbnid=KQI5AbkkVp3-uM%3A&zoom=1&docid=6Bd7CTaQ291_UM&ei=5AU0VceoI87WPYOvgCg&tbm=isch&iact=rc&uact=3&dur=3255&page=1&start=0&ndsp=20&ved=0CDYQrQMwBw");
a.setBiography(biography);
temp.add(a);
System.out.println("FAAT" + a.getTitle());
}
return temp;
}
private String addPrefix(String prefix) { return "PREFIX " + prefix + "\n"; }
private String addQuery(String query) { return query; }
}
好吧,我在记录了几件事后发现了。。。首先,我记录了结果集的大小,使用可选的过滤器,它给了我比没有可选过滤器时更多的结果。。。2383对2103,不带选装件。。然后我注意到如果 a、 setPictureURLrow.getthumb2.toString;如果为空或null,循环将不会继续。。。它在14次结果后停止,并没有给我这种方法的回报:
private LinkedList<Entity> collectAuthors(ResultSet results) {
LinkedList<Entity> temp = new LinkedList<>();
while (results.hasNext()) {
Entity a = new Entity();
QuerySolution row = results.next();
String fullName = row.get("name").toString().substring(0, row.get("name").toString().indexOf("@"));
String biography = row.get("desc").toString().substring(0, row.get("desc").toString().indexOf("@"));
a.setTitle(fullName);
a.setWikiID(Integer.parseInt(row.get("wiki").toString().substring(0, row.get("wiki").toString().indexOf("^"))));
if (!row.get("thumb").toString().isEmpty())
a.setPictureURL(row.get("thumb").toString());
a.setBiography(biography);
temp.add(a);
System.out.println("FAAT" + a.getTitle());
}
return temp;
}
然后循环问题就解决了
谢谢大家的提示,请注意空的reslutset列,以Jena作为旁白,连接字符串的方式非常容易出错。如果语言或关键字包含字符,会发生什么情况?另外,您不应该将语言标记与lang…=。。。,但是使用langMatcheslang…,…谢谢你的建议,我会修改它,但我目前的主要问题是这个可选的,我还希望返回没有拇指的实体:就像在snorql示例中一样…使用本体更改可选的:缩略图。这可能会得到解决。还有,它会产生什么样的错误?@Artemis我同意ontology:thumbnail是更好的样式,因为前缀是定义的,但它是相同的URI,所以这不会有什么区别。你认为结果为零吗,或者你有什么错误吗?你应该接受你自己的答案,以备将来参考。我需要等两天,因为我没有得到足够的贡献。。。但你也应该接受它:@StackItEasy你是唯一能接受你问题答案的人;我们其他人只能投赞成票或反对票;在这个问题上我看不到拇指2;只要拇指。拇指2是在哪里起作用的?