Unify Frequently Asked Questions

Does your identity model support multiple external ID types?

Yes, Identity Graph supports multiple external IDs.

Identity Graph automatically collects a rich set of external IDs without any additional code:

1. Device level IDs (ex: anonymous_id, ios.idfa and android.id)
2. Device token IDs (ex: ios.push_token and android_push_token)
3. User level IDs (ex: user_id)
4. Common external IDs (email)
5. Cross domain analytics IDs (cross_domain_id)

If you want Identity Graph to operate on a different custom ID, you can pass it in using context.externalIds on an identify() or track(). If you’re interested in this feature, contact your CSM to discuss the best way to implement this feature.

How does Unify handle identity merging?

Each incoming event is analyzed and external IDs are extracted (user_id, anonymous_id, email). The simplified algorithm works as follows:

1. Segment first searches the Identity Graph for incoming external IDs.
2. If Segment finds no matching profile(s), it creates one.
3. If Segment finds one profile, it merges the incoming event with that profile. (This means that Segment adds the external IDs on the incoming message and resolves the event to the profile.)
4. If Segment finds multiple matching profiles, Segment applies the identity resolution settings for merge protection. Specifically, Segment uses identifier limits and priorities to add the correct identifiers to the profile.
5. Segment then applies limits to ensure profiles remain under these limits. Segment doesn’t add any further merges or mappings if the profile is at either limit, but event resolution for the profile will continue.

Is all matching deterministic, or is there any support for probabilistic matching?

All Profile matching is deterministic and based on first-party data that you’ve collected.

Segment doesn’t support probabilistic matching. Most marketing automation use cases require 100% confidence that a user is who you think they are (sending an email, delivering a recommendation, and so on). The best way to support this is through a deterministic identity algorithm.

What happens to conflicting and non-conflicting profile attributes?

If two merged user profiles contain conflicting profile attributes, Segment selects the newest, or last updated, attributes when querying the profile.

What identifiers can the merged profile be queried/updated with?

Any of the external IDs can be used to query a profile. When a profile is requested, Segment traverses the merge graph and resolves all merged profiles. The result is a single profile, with the latest state of all traits, events, and identifiers.

Can ExternalID’s be changed or removed from the profiles?

No. As the Identity Graph uses ExternalIDs, they remain for the lifetime of the user profile.