zoukankan      html  css  js  c++  java
  • ES 相似度算法设置(续)

    Tuning BM25

    One of the nice features of BM25 is that, unlike TF/IDF, it has two parameters that allow it to be tuned:

    k1
    This parameter controls how quickly an increase in term frequency results in term-frequency saturation. The default value is 1.2. Lower values result in quicker saturation, and higher values in slower saturation.
    b
    This parameter controls how much effect field-length normalization should have. A value of 0.0disables normalization completely, and a value of 1.0 normalizes fully. The default is 0.75.

    The practicalities of tuning BM25 are another matter. The default values for k1 and b should be suitable for most document collections, but the optimal values really depend on the collection. Finding good values for your collection is a matter of adjusting, checking, and adjusting again.

    The similarity algorithm can be set on a per-field basis. It’s just a matter of specifying the chosen algorithm in the field’s mapping:

    PUT /my_index
    {
      "mappings": {
        "doc": {
          "properties": {
            "title": {
              "type":       "string",
              "similarity": "BM25" 
            },
            "body": {
              "type":       "string",
              "similarity": "default" 
            }
          }
      }
    }

    The title field uses BM25 similarity.

    The body field uses the default similarity (see Lucene’s Practical Scoring Function).

    Currently, it is not possible to change the similarity mapping for an existing field. You would need to reindex your data in order to do that.

    Configuring BM25

    Configuring a similarity is much like configuring an analyzer. Custom similarities can be specified when creating an index. For instance:

    PUT /my_index
    {
      "settings": {
        "similarity": {
          "my_bm25": { 
            "type": "BM25",
            "b":    0 
          }
        }
      },
      "mappings": {
        "doc": {
          "properties": {
            "title": {
              "type":       "string",
              "similarity": "my_bm25" 
            },
            "body": {
              "type":       "string",
              "similarity": "BM25" 
            }
          }
        }
      }
    }

    参考:https://www.elastic.co/guide/en/elasticsearch/guide/current/changing-similarities.html
  • 相关阅读:
    把word文档转换成swf格式
    利用“审阅”批改作业
    注意:QQ空间加密并不安全
    MySQLDB 错误 InterfaceError(0,")
    Linux 文件大小 文件夹大小 磁盘大小
    JavaArrays类fill()方法详解
    构造函数
    ASP部署错误"未能加载类型..."
    试AJAX出错两则
    ASP.Net如何区分开发状态与实际应用状态
  • 原文地址:https://www.cnblogs.com/bonelee/p/6472828.html
Copyright © 2011-2022 走看看