7.14.17. snippet_html

7.14.17.1. Summary

snippet_html extracts snippets of target text around search keywords (KWIC. KeyWord In Context). The snippets are prepared for embedding HTML. Special characters such as < and > are escapsed as &lt; and &gt;. Keyword is surrounded with <span class="keyword"> and </span>. For example, a snippet of I am a groonga user. <3 for keyword groonga is I am a <span class="keyword">groonga</span> user. &lt;3.

7.14.17.2. Syntax

snippet_html has only one parameter:

snippet_html(column)

snippet_html has many parameters internally but they can't be specified for now. You will be able to custom those parameters soon.

7.14.17.3. Usage

Here are a schema definition and sample data to show usage.

Execution example:

table_create Documents TABLE_NO_KEY
# [[0, 1337566253.89858, 0.000355720520019531], true]
column_create Documents content COLUMN_SCALAR Text
# [[0, 1337566253.89858, 0.000355720520019531], true]
table_create Terms TABLE_PAT_KEY ShortText --default_tokenizer TokenBigram --normalizer NormalizerAuto
# [[0, 1337566253.89858, 0.000355720520019531], true]
column_create Terms documents_content_index COLUMN_INDEX|WITH_POSITION Documents content
# [[0, 1337566253.89858, 0.000355720520019531], true]
load --table Documents
[
["content"],
["Groonga is a fast and accurate full text search engine based on inverted index. One of the characteristics of groonga is that a newly registered document instantly appears in search results. Also, groonga allows updates without read locks. These characteristics result in superior performance on real-time applications."],
["Groonga is also a column-oriented database management system (DBMS). Compared with well-known row-oriented systems, such as MySQL and PostgreSQL, column-oriented systems are more suited for aggregate queries. Due to this advantage, groonga can cover weakness of row-oriented systems."]
]
# [[0, 1337566253.89858, 0.000355720520019531], 2]

snippet_html can be used in only --output_columns in select.

You also need to specify --query and/or --filter. Keywords are extracted from --query and --filter arguments.

The following example uses --query "fast performance". In this case, fast and performance are used as keywords.

Execution example:

select Documents --output_columns "snippet_html(content)" --command_version 2 --match_columns content --query "fast performance"
# [
#   [
#     0,
#     1337566253.89858,
#     0.000355720520019531
#   ],
#   [
#     [
#       [
#         1
#       ],
#       [
#         [
#           "snippet_html",
#           "null"
#         ]
#       ],
#       [
#         [
#           "Groonga is a <span class=\"keyword\">fast</span> and accurate full text search engine based on inverted index. One of the characteristics of groonga is that a newly registered document instantly appears in search results. Also, gro",
#           "onga allows updates without read locks. These characteristics result in superior <span class=\"keyword\">performance</span> on real-time applications."
#         ]
#       ]
#     ]
#   ]
# ]

--query "fast performance" matches to only the first record's content. snippet_html(content) extracts two text parts that include the keywords fast or performance and surrounds the keywords with <span class="keyword"> and </span>.

The max number of text parts is 3. If there are 4 or more text parts that include the keywords, only the leading 3 parts are only used.

The max size of a text part is 200byte. The unit is bytes not characters. The size doesn't include inserted <span keyword="keyword"> and </span>.

Both the max number of text parts and the max size of a text part aren't customizable.

You can specify string literal instead of column.

Execution example:

select Documents --output_columns 'snippet_html("Groonga is very fast fulltext search engine.")' --command_version 2 --match_columns content --query "fast performance"
# [
#   [
#     0,
#     1337566253.89858,
#     0.000355720520019531
#   ],
#   [
#     [
#       [
#         1
#       ],
#       [
#         [
#           "snippet_html",
#           "null"
#         ]
#       ],
#       [
#         [
#           "Groonga is very <span class=\"keyword\">fast</span> fulltext search engine."
#         ]
#       ]
#     ]
#   ]
# ]

7.14.17.4. Return value

snippet_html returns an array of string or null. If snippet_html can't find any snippets, it returns null.

An element of array is a snippet:

[SNIPPET1, SNIPPET2, SNIPPET3]

A snippet includes one or more keywords. The max byte size of a snippet except <span keyword="keyword"> and </span> is 200byte. The unit isn't the number of characters.

The array size is larger than or equal to 0 and less than or equal to 3. The max size 3 will be customizable soon.

7.14.17.5. TODO

  • Make the max number of text parts customizable.
  • Make the max size of a text part customizable.
  • Make keywords customizable.
  • Make tag that surrounds a keyword customizable.
  • Make normalization customizable.
  • Support options by object literal.

7.14.17.6. See also