# groonga - An open-source fulltext search engine and column store.

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# 8.8.1. QueryExpanderTSV

## 8.8.1.1. Summary

`QueryExpanderTSV` is a query expander plugin that reads synonyms from TSV (Tab Separated Values) file. This plugin provides poor feature than the embedded query expansion feature. For example, it doesn't support word normalization. But it may be easy to use because you can manage your synonyms by TSV file. You can edit your synonyms by spreadsheet application such as Excel. With the embedded query expansion feature, you manage your synonyms by groonga's table.

## 8.8.1.2. Install

You need to register `query_expanders/tsv` as a plugin before you use `QueryExpanderTSV`:

    register query_expanders/tsv

## 8.8.1.3. Usage

You just add `--query_expansion QueryExpanderTSV` parameter to `select` command:

    select --query "QUERY" --query_expansion QueryExpanderTSV

If `QUERY` has registered synonyms, they are expanded. For example, there are the following synonyms.

word | synonym 1 | synonym 2
--- | --- | ---
groonga | groonga | Senna
mroonga | mroonga | groonga MySQL

The table means that `synonym 1` and `synonym 2` are synonyms of `word`. For example, `groonga` and `Senna` are synonyms of `groonga`. And `mroonga` and `groonga MySQL` are synonyms of `mroonga`.

Here is an example of query expnasion that uses `groonga` as query:

    select --query "groonga" --query_expansion QueryExpanderTSV

The above command equals to the following command:

    select --query "groonga OR Senna" --query_expansion QueryExpanderTSV

Here is another example of query expnasion that uses `mroonga search` as query:

    select --query "mroonga search" --query_expansion QueryExpanderTSV

The above command equals to the following command:

    select --query "(mroonga OR (groonga MySQL)) search" --query_expansion QueryExpanderTSV

It is important that registered words (`groonga` and `mroonga`) are only expanded to synonyms and not registered words (`search`) are not expanded. Query expansion isn't occurred recursively. `groonga` is appeared in `(mroonga OR (groonga MySQL))` as query expansion result but it isn't expanded.

Normally, you need to include `word` itself into synonyms. For example, `groonga` and `mroonga` are included in synonyms of themselves. If you want to ignore `word` itself, you don't include `word` itself into synonyms. For example, if you want to use query expansion as spelling correction, you should use the following synonyms.

word | synonym
--- | ---
gronga | groonga

`gronga` in `word` has a typo. A `o` is missing. `groonga` in `synonym` is the correct word.

Here is an example of using query expnasion as spelling correction:

    select --query "gronga" --query_expansion QueryExpanderTSV

The above command equals to the following command:

    select --query "groonga" --query_expansion QueryExpanderTSV

The former command has a typo in `--query` value but the latter command doesn't have any typos.

## 8.8.1.4. TSV File

Synonyms are defined in TSV format file. This section describes about it.

### 8.8.1.4.1. Location

The file name should be `synonyms.tsv` and it is located at configuration directory. For example, `/etc/groonga/synonyms.tsv` is a TSV file location. The location is decided at build time.

You can change the location by environment variable `GRN_QUERY_EXPANDER_TSV_SYNONYMS_FILE` at run time:

    % env GRN_QUERY_EXPANDER_TSV_SYNONYMS_FILE=/tmp/synonyms.tsv groonga

With the above command, `/tmp/synonyms.tsv` file is used.

### 8.8.1.4.2. Format

You can define zero or more synonyms in a TSV file. You define a `word` and `synonyms` pair by a line. `word` is expanded to `synonyms` in `--query` value. `Synonyms` are combined by `OR`. For example, `groonga` and `Senna` synonyms are expanded as `groonga OR Senna`.

The first column is `word` and the rest columns are `synonyms` of the `word`. Here is a sample line for `word` is `groonga` and `synonyms` are `groonga` and `Senna`. `(TAB)` means a tab character (`U+0009`):

    groonga(TAB)groonga(TAB)Senna

Comment line is supported. Lines that start with `#` are ignored. Here is an example for comment line. `groonga` line is ignored as comment line:

    #groonga(TAB)groonga(TAB)Senna
    mroonga(TAB)mroonga(TAB)groonga MySQL

## 8.8.1.5. Limitation

You need to restart groonga to reload your synonyms. TSV file is loaded only at the plugin load time.

## 8.8.1.6. See also

> - query_expansion

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