17种文本相似算法与GIN索引 - pg_similarity

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背景

文本相似算法,结合PostgreSQL的开放索引框架GIN,可以实现各种相似算法的文本高效检索。

PostgreSQL中常见的文本相似搜索插件:rum, pg_trgm, fuzzymatch, pg_similarity, smlar。

其中pg_similarity支持的算法达到了17种。

Introduction

pg_similarity is an extension to support similarity queries on PostgreSQL.

The implementation is tightly integrated in the RDBMS in the sense that it defines operators
so instead of the traditional operators (= and <>) you can use ~~~ and ~!~ (any of these
operators represents a similarity function).

pg_similarity has three main components:

Functions:

a set of functions that implements similarity algorithms available in the literature.

These functions can be used as UDFs and, will be the base for implementing the similarity operators;

Operators:

a set of operators defined at the top of similarity functions.

They use similarity functions to obtain the similarity threshold and,
compare its value to a user-defined threshold to decide if it is a match or not;

Session Variables:

a set of variables that store similarity function parameters. Theses variables can be defined at run time.

  • L1 Distance (as known as City Block or Manhattan Distance);
  • Cosine Distance;
  • Dice Coefficient;
  • Euclidean Distance;
  • Hamming Distance;
  • Jaccard Coefficient;
  • Jaro Distance;
  • Jaro-Winkler Distance;
  • Levenshtein Distance;
  • Matching Coefficient;
  • Monge-Elkan Coefficient;
  • Needleman-Wunsch Coefficient;
  • Overlap Coefficient;
  • Q-Gram Distance;
  • Smith-Waterman Coefficient;
  • Smith-Waterman-Gotoh Coefficient;
  • Soundex Distance.

用法如下

Algorithm Function Operator Use Index? Parameters
L1 Distance block(text, text) returns float8 ~++ yes pg_similarity.block_tokenizer (enum)
pg_similarity.block_threshold (float8)
pg_similarity.block_is_normalized (bool)
Cosine Distance cosine(text, text) returns float8 ~## yes pg_similarity.cosine_tokenizer (enum)
pg_similarity.cosine_threshold (float8)
pg_similarity.cosine_is_normalized (bool)
Dice Coefficient dice(text, text) returns float8 ~-~ yes pg_similarity.dice_tokenizer (enum)
pg_similarity.dice_threshold (float8)
pg_similarity.dice_is_normalized (bool)
Euclidean Distance euclidean(text, text) returns float8 ~!! yes pg_similarity.euclidean_tokenizer (enum)
pg_similarity.euclidean_threshold (float8)
pg_similarity.euclidean_is_normalized (bool)
Hamming Distance hamming(bit varying, bit varying) returns float8
hamming_text(text, text) returns float8
~@~ no pg_similarity.hamming_threshold (float8)
pg_similarity.hamming_is_normalized (bool)
Jaccard Coefficient jaccard(text, text) returns float8 ~?? yes pg_similarity.jaccard_tokenizer (enum)
pg_similarity.jaccard_threshold (float8)
pg_similarity.jaccard_is_normalized (bool)
Jaro Distance jaro(text, text) returns float8 ~%% no pg_similarity.jaro_threshold (float8)
pg_similarity.jaro_is_normalized (bool)
Jaro-Winkler Distance jarowinkler(text, text) returns float8 ~@@ no pg_similarity.jarowinkler_threshold (float8)
pg_similarity.jarowinkler_is_normalized (bool)
Levenshtein Distance lev(text, text) returns float8 ~== no pg_similarity.levenshtein_threshold (float8)
pg_similarity.levenshtein_is_normalized (bool)
Matching Coefficient matchingcoefficient(text, text) returns float8 ~^^ yes pg_similarity.matching_tokenizer (enum)
pg_similarity.matching_threshold (float8)
pg_similarity.matching_is_normalized (bool)
Monge-Elkan Coefficient mongeelkan(text, text) returns float8 ~|| no pg_similarity.mongeelkan_tokenizer (enum)
pg_similarity.mongeelkan_threshold (float8)
pg_similarity.mongeelkan_is_normalized (bool)
Needleman-Wunsch Coefficient needlemanwunsch(text, text) returns float8 ~#~ no pg_similarity.nw_threshold (float8)
pg_similarity.nw_is_normalized (bool)
Overlap Coefficient overlapcoefficient(text, text) returns float8 ~** yes pg_similarity.overlap_tokenizer (enum)
pg_similarity.overlap_threshold (float8)
pg_similarity.overlap_is_normalized (bool)
Q-Gram Distance qgram(text, text) returns float8 ~~~ yes pg_similarity.qgram_threshold (float8)
pg_similarity.qgram_is_normalized (bool)
Smith-Waterman Coefficient smithwaterman(text, text) returns float8 ~=~ no pg_similarity.sw_threshold (float8)
pg_similarity.sw_is_normalized (bool)
Smith-Waterman-Gotoh Coefficient smithwatermangotoh(text, text) returns float8 ~!~ no pg_similarity.swg_threshold (float8)
pg_similarity.swg_is_normalized (bool)
Soundex Distance soundex(text, text) returns float8 ~*~ no

参考

http://pgsimilarity.projects.pgfoundry.org/

https://github.com/eulerto/pg_similarity

https://www.pgcon.org/2009/schedule/attachments/108_pg_similarity.pdf

http://www.sigaev.ru/git/gitweb.cgi?p=smlar.git;a=summary

https://github.com/postgrespro/rum

https://www.postgresql.org/docs/9.6/static/fuzzystrmatch.html

https://www.postgresql.org/docs/9.6/static/pgtrgm.html

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