# Identifiers

**Identifiers** are how we connect objects to an [**Identity**](https://dfend.gitbook.io/documentation/developer-api/types/identity). The Identifiers object is present on both [**Signals**](https://dfend.gitbook.io/documentation/developer-api/types/signal) and [**Identities**](https://dfend.gitbook.io/documentation/developer-api/types/identity) in some form.

Identifier fields fall into two subtypes: primary and secondary. Primary identifiers are reliably unique, whereas secondary identifiers can be used for some matching operations but are not expected to always be unique.

## Attributes

### Primary identifiers

Either one of these is required for any operation connected to an Identity.

* `userId`  <mark style="color:blue;">string</mark>  The user's primary key or unique ID in your system.
* `identity`  <mark style="color:blue;">string</mark>  The `id` value of the user's [Identity](https://dfend.gitbook.io/documentation/developer-api/types/identity) in DFend.

### Secondary identifiers

None of these are required, but they can improve matching and reduce the occurrence of duplicate Identities.

* `phone`  <mark style="color:blue;">string</mark>  The user's phone number. Must be in [E. 164 format](https://www.twilio.com/docs/glossary/what-e164).
* `email`  <mark style="color:blue;">string</mark>  The user's email address. Must be a valid email address.
* `name`  <mark style="color:blue;">string</mark>  The user's name.