Ranking formula

Available in Classic and VPC

You can utilize ranking formulas to sort your search results the way you want. This describes how to create ranking formulas and apply them when searching.

Ranking formula

A ranking formula is an expression to calculate a ranking score that is the criterion to sort search results. Ranking scores are usually expressed as relevance (_relevance) and calculated as the sum of similarity (_similarity) and quality (_quality).
<Example> Ranking formula of the basic ranking (clous) provided upon creation of domain

_ratio=0.5;
_quality=1.0;
_similarity=qds;
_relevance = _similarity * _ratio + _quality * (1 - _ratio);

You can write your own ranking formula to sort your search results in an order appropriate for each search service.

Writing a ranking formula

The way to write a ranking formula is as follows.

• Use only assignment statements in the form of a single function.

  relevance = qds;
  relevance() = qds; // exactly the same as above.
  relevance( x ) = x*qds;
  

• Enter all lines as a string separated by semicolons (;).
• Write using various variables, attribute values, expressions, and built-in functions.
  <Example> Example of writing a ranking formula

  relevance = min(qry_mtc("q1"), qry_mtc("q2"));
  normalized_qds = qds/qtermc;
  normalized_qds_of_q1 = qry_qds("q1") / qry_qtermc("q1");
  mtratio = mtc/qtermc;
  

Ranking variables and attribute values

When creating ranking formulas, you can use various attribute values along with ranking variables.

Ranking variables

Available ranking variables when creating a ranking formula are as follows.

• A function with document attribute values (dp_섹션이름): a ranking variable set when creating a section
  <Example> Ranking formula with document attribute values

  _ratio=0.5;
  _quality= dp_like_cnt * 0.09 + dp_dislike_cnt * 0.01;
  _similarity=qds;
  _relevance = _similarity * _ratio + _quality * (1 - _ratio);
  

• Define the desired variables

Query property

Available property values of queries when creating a ranking formula are as follows.

• qtermc: the number of search words of a query, the number of added search words (Query-Term-Count) to qds
• qry_qtermc(query_name): the number of search words of a specific query (query_name), a compound query is used to obtain the number of search words of individual queries
• qry_exist(query_name): return whether a specific query (query_name) exists
• epoch_time: the time at the start of executing a query

Document score

Available property values of documents when creating a ranking formula are as follows.

• qds: document weight, similarity of query document (Query-Document-Score)
• qry_qds(query_name): document weight for a specific query (query_name)
• mtc: the number of query terms included in the search target documents (Matched-Term-Count)
• qry_mtc(query_name): the number of query terms included in the search target document for a specific query (query_name) (mtc)

Other

Other available property values when creating a ranking formula are as follows.

• total_document_count: total number of search result documents (estimated)
  • The total number of documents is subject to change when requests for uploading document are in progress.

Expressions and built-in functions

You can use a variety of expressions and built-in functions when writing ranking formulas.

Expressions

Available expressions when creating a ranking formula are as follows.

• Arithmetic operators: +, -, *, /
• Comparison operators: >, <, >=, <=, ==, !=
• Logical operators: |, &, !
• Constant expressions: integer, real, true, false
• Condition expressions: if - then - else

<Example> Ranking formula written in an expression

mtr = mtc/qtermc;
quality = 1.0;
relevance = if mtr >= 0.6 then qds + quality else quality;

Built-in functions

Available built-in functions when creating a ranking formula are as follows.

• min(a, b): minimum value
• max(a, b): maximum value
• exp(x): index
• log(x): natural logarithm
• log10(x): log
• sqrt(x): square root
• pow(x, y): y-square of x

Using ranking formula

You can use the created ranking formula by writing a search query during search as follows.

• If you save the ranking formula in the ranking module
  • Specifies the ranking module to use in the ranking field
  • Specifies the ranking variable calculated in the ranking formula as a parameter of the sort field
    • If you set the ranking module to the default, you are not required to set up the ranking field.
• If you enter a ranking formula directly into your search query
  • Enter the ranking formula directly in the ranking field
  • Specifies the ranking variable calculated in the ranking formula as a parameter of the sort field

<Example> Search query that specifies the ranking variable (relevance) of the basic ranking as a sort field parameter

{
  "search": {
    "index_name": {
      "main": [
        {
          "name": "q1",
          "query": "term"
        },
        {
          "name": "q2",
          "query": "test"
        }
      ]
    }
  },
  "sort" : {
    "relevance": "desc"
  }
}