DataparkSearch Engine 4.26 reference manual: The Web searching software
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# Chapter 6. Subsections

# Tags

Tag is a special parameter which can be given for a set of documents. The main purpose of tags is to join a number of documents into one group and then while doing search to select a group of documents to search through.

You can use Tag command of `indexer.conf` to give some tag value for a server or server subset. While doing search you can specify tag value to search through documents which tag matches given parameter with `t=xxx` parameter, which can be passed from HTML form. Take a look into the Section called Tag command in Chapter 3, `indexer.conf-dist` and `search.htm-dist` for explanation and examples.

## Tags in SQL version

Tag type is CHAR. CHAR type allows to use some nice features. You can use '_' and '%' LIKE wildcards in tag parameter when doing search. It makes possible that tag, like a category, does support an idea of nesting. For example, documents with tag value "AB" can be found with both "A%" and "AB" tag limits.

Tags also give a way to make an URL a member of multiple tag selections. Playing with LIKE wildcards you can easily create two or more groups.

For example, tag "ABCDE" is the member of at least these selections:

    _BCDE
    A_CDE
    AB_DE
    ABC_E
    ABCD_

> Note: If you have big enough database and often use tag limits, it is useful to create an index by field "tag" in "server" table. This index is not created by default.

>     CREATE INDEX srv_tag ON "server" ("tag");

> By default, the length of tag field in url table is limited by 16 characters. If you need more, increase this length before DB creating.

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