Compare the Default and High-fidelity or Custom ID strategies, and choose the one that matches how you collect and use identifiers.
Your ID strategy decides which identifiers Zeotap trusts to resolve an incoming record to a customer profile — see Identity Resolution for what that resolution does — and you choose one of two: Default or High-fidelity or Custom.
Every identifier starts as Disabled — including ones added to your catalogue later — and takes no part in resolution until you classify it.
Records carrying no usable identifier
Any identifier can create a profile, so this does not arise.
A record carrying only Disabled identifiers is not ingested.
When several profiles match one record
The profile with the first created UCID is kept as the master and the others merge into it.
The same, unless you set different priorities within a classification — then the profile matched by the highest-priority identifier becomes the master. See ID Prioritisation.
Usually one, as broadly as the shared identifiers allow — though delayed linkage information can create several UCIDs, which are then reconciled into the first created one.
Depending on how you classify your identifiers, there can be more than one.
NoteIdentifiers you classify as Disabled are still ingested and stored against the profile, and stay available downstream — being Disabled only keeps them out of identity resolution.
Much of your traffic is anonymous, and you want that behaviour attached to known profiles automatically.
You hold few known first-party identifiers, and mostly anonymous or third-party ones.
You want the simplest possible setup, with no classification to maintain.
The trade-off is control. Because every identifier is trusted equally, identifiers that several people share can pull distinct customers into one profile — which also makes this strategy a poor fit for one-to-one personalisation, where a message must reach exactly the right person. For how it behaves, see Default ID Strategy.
The High-fidelity or Custom strategy suits you if:
You hold rich first-party data, with an identifier that reliably identifies one person.
You need highly accurate profiles for one-to-one use cases such as personalised email.
Anonymous and logged-in users carry different consent or privacy requirements in your business.
Your industry does not enforce one identifier per account — where the same email address can be used for several accounts, for example.
You want the profile merge decision to be yours, with attribution back to the exact customer.
The trade-off is preparation. The quality of your profiles depends on your Primary identifiers being populated — which matters most for file-based ingestion — and, depending on how you classify, one person may hold more than one profile. For how it behaves, see High-fidelity or Custom ID Strategy.
Choose deliberately. An ID strategy can be changed later, but the change is not retrospective — it applies only to records ingested after it, so profiles already resolved keep the UCIDs they were given. The change also triggers a reindex that pauses ingestion across your sources while it runs, so plan it for a maintenance window. See Edit an ID Strategy.
