7.15.22. snippet_html¶
7.15.22.1. Summary¶
This function 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 < and >. 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. <3.
This function is a HTML specific version of snippet. Generally, this function is enough for normal Web application use.
7.15.22.2. Syntax¶
snippet_html has only one parameter:
snippet_html(column)
7.15.22.3. 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 class="keyword">
and </span>.
Both the max number of text parts and the max size of a text part aren’t customizable.
If you want to customize them, you need to use snippet instead of this function.
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."
# ]
# ]
# ]
# ]
# ]
7.15.22.4. Return value¶
This function returns an array of string or null. If This function
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 open tag and close tag is 200byte. The unit isn’t the number of characters.
Open tag is <span class="keyword"> and close tag is </span>.
The array size is larger than or equal to 1 and less than or equal to 3.
If you want to customize the max byte size of snippet and/or the max number of snippets, use snippet instead.