# Activate Synonyms in an IDOL Server

This solution is the easiest of the three synonym choices to implement, but is useful only if you require synonym matching for a maximum of approximately 100 terms. Beyond this limit, query response times experience a growing increase with the number of synonym terms, and it can have a negative impact on indexing performance.

Internal synonyms introduce the concept of expansion level; that is, the conceptual distance between synonyms. A synonym that you specify explicitly has an expansion level of zero. You can then expand the synonyms again, to get further expansions. For example, if there is a hierarchy of synonyms such that terrier expands to dog, and dog expands to animal, then:

- terrier to dog has an expansion level of zero.

- dog to animal also has an expansion level of zero.

- terrier to animal has an expansion level of one.

## Configuration

To use synonyms in an IDOL Server, you must configure the `[Synonym]` section in the IDOL or Content server configuration file. In this section, you configure a list of synonym jobs, which are run at query time.

Each synonym job defines a file, which has a list of synonyms to process, and the `MaxExpandLevel`. For example:

    [Synonym]
    0=PC_Syn

    [PC_Syn]
    File=myfile.txt
    MaxExpandLevel=1

The referenced file must contain comma-separated lists of synonymous terms and phrases for a particular language type. For example, `myfile.txt` might contain synonyms for animals:

    [EnglishUTF8]
    dog,canine,puppy,hound,wolf
    cat,feline,kitten,kitty

You must also apply the `SynonymType` field property to any fields that you want to perform synonym expansion on. For example:

    [FieldProcessing]
    ...
    19=SynonymMatch

    // Specify the fields that synonym expansion will be performed on
    [SynonymMatch]
    Property=ApplySynonymMatch
    PropertyFieldCSVs=*/DRETITLE,*/DRECONTENT

    // Specify the synonym job to apply to those fields
    [ApplySynonymMatch]
    SynonymType=PC_Syn

## Usage

After synonyms have been activated, you can use them by setting the `Synonym` action parameter to `True` in the `Query` action.

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