# ReferenceType Fields

`ReferenceType` fields are used to identify documents. Before you index a document into the IDOL Content component, you have to set up a field process that determines which of the fields in a document are used as its `ReferenceType` field (note that a document can have multiple `ReferenceType` fields).

At index time, you can use `ReferenceType` fields to eliminate duplicate copies of documents. At query time, you can use `ReferenceType` fields to filter results (for example, by using the `Combine` action parameter or by specifying references that results must or must not match).

Note that if you want to eliminate duplicate document copies and use the `Combine` action parameter, you must set up separate `ReferenceType` fields for these processes.

Related Topics

- Prevent Duplicate Documents

- Combine Parameter

- Use KillDuplicates and Combine on ReferenceType Fields

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