lucene - 给予更多权重,更接近的术语是标题的开头

Question

我了解如何在索引时或查询时提升字段.但是,如何才能增加匹配一个更接近标题开头的术语的分数？

例:

Query = "lucene"

Doc1 title = "Lucene: Homepage"
Doc2 title = "I have a question about lucene?"

我希望第一个文件得分更高,因为"lucene"更接近开头(暂时忽略术语频率).

我看到如何使用SpanQuery来指定术语之间的接近程度,但我不确定如何使用有关该字段中位置的信息.

我在Java中使用Lucene 4.1.

Answer 1

我会使用a SpanFirstQuery,它匹配字段开头附近的术语.由于所有跨度查询都依赖于位置,默认情况下在lucene中进行索引时启用.

让我们独立测试它:您只需要提供您SpanTermQuery可以找到该术语的最大位置(在我的示例中为一个).

SpanTermQuery spanTermQuery = new SpanTermQuery(new Term("title", "lucene"));
SpanFirstQuery spanFirstQuery = new SpanFirstQuery(spanTermQuery, 1);

鉴于您的两个文档,此查询将只找到标题为"Lucene:Homepage"的第一个文档,如果您使用标题进行分析StandardAnalyzer.

现在我们可以以某种方式将上述内容SpanFirstQuery与普通文本查询相结合,并使第一个仅影响分数.您可以使用a轻松执行此操作BooleanQuery并将span查询作为should子句,如下所示:

Term term = new Term("title", "lucene");
TermQuery termQuery = new TermQuery(term);
SpanFirstQuery spanFirstQuery = new SpanFirstQuery(new SpanTermQuery(term), 1);
BooleanQuery booleanQuery = new BooleanQuery();
booleanQuery.add(new BooleanClause(termQuery, BooleanClause.Occur.MUST));
booleanQuery.add(new BooleanClause(spanFirstQuery, BooleanClause.Occur.SHOULD));

可能有不同的方法来实现相同,可能使用CustomScoreQuery太多或自定义代码来实现评分,但在我看来这是最简单的.

我用来测试它的代码打印下面的输出(包括得分)执行唯一的TermQuery第一个,然后是唯一的SpanFirstQuery,最后是组合的BooleanQuery:

------ TermQuery --------
Total hits: 2
title: I have a question about lucene - score: 0.26010898
title: Lucene: I have a really hard question about it - score: 0.22295055
------ SpanFirstQuery --------
Total hits: 1
title: Lucene: I have a really hard question about it - score: 0.15764984
------ BooleanQuery: TermQuery (MUST) + SpanFirstQuery (SHOULD) --------
Total hits: 2
title: Lucene: I have a really hard question about it - score: 0.26912516
title: I have a question about lucene - score: 0.09196242

这是完整的代码:

public static void main(String[] args) throws Exception {

        Directory directory = FSDirectory.open(new File("data"));

        index(directory);

        IndexReader indexReader = DirectoryReader.open(directory);
        IndexSearcher indexSearcher = new IndexSearcher(indexReader);

        Term term = new Term("title", "lucene");

        System.out.println("------ TermQuery --------");
        TermQuery termQuery = new TermQuery(term);
        search(indexSearcher, termQuery);

        System.out.println("------ SpanFirstQuery --------");
        SpanFirstQuery spanFirstQuery = new SpanFirstQuery(new SpanTermQuery(term), 1);
        search(indexSearcher, spanFirstQuery);

        System.out.println("------ BooleanQuery: TermQuery (MUST) + SpanFirstQuery (SHOULD) --------");
        BooleanQuery booleanQuery = new BooleanQuery();
        booleanQuery.add(new BooleanClause(termQuery, BooleanClause.Occur.MUST));
        booleanQuery.add(new BooleanClause(spanFirstQuery, BooleanClause.Occur.SHOULD));
        search(indexSearcher, booleanQuery);
    }

    private static void index(Directory directory) throws Exception {
        IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_41, new StandardAnalyzer(Version.LUCENE_41));

        IndexWriter writer = new IndexWriter(directory, config);

        FieldType titleFieldType = new FieldType();
        titleFieldType.setIndexOptions(FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS);
        titleFieldType.setIndexed(true);
        titleFieldType.setStored(true);

        Document document = new Document();
        document.add(new Field("title","I have a question about lucene", titleFieldType));
        writer.addDocument(document);

        document = new Document();
        document.add(new Field("title","Lucene: I have a really hard question about it", titleFieldType));
        writer.addDocument(document);

        writer.close();
    }

    private static void search(IndexSearcher indexSearcher, Query query) throws Exception {
        TopDocs topDocs = indexSearcher.search(query, 10);

        System.out.println("Total hits: " + topDocs.totalHits);

        for (ScoreDoc hit : topDocs.scoreDocs) {
            Document result = indexSearcher.doc(hit.doc);
            for (IndexableField field : result) {
                System.out.println(field.name() + ": " + field.stringValue() +  " - score: " + hit.score);
            }
        }
    }