You can either use the Default Strategy or choose to configure the Custom or High-Fidelity Strategy.

For the Default Strategy, any identifier attribute received across the sources is used to identify a customer profile or create a new profile.
For the Custom or High-Fidelity Strategy, you have to start by classifying your IDs. By default, all the IDs in your catalogue are marked as Secondary. You can change the selection to Primary as required.

Primary or Secondary, they appear in the respective buckets. By default, all the IDs in the respective buckets, are assigned priority 1. Next, you can define the priority of your IDs as follows:
- You can either change the classification of the IDs by dropping them from one bucket to the other.
- Or, set the priority within the bucket. You can set the same or different priority among IDs within a classification. Zeotap allows you to define priority up to level five.

Note:Here are some quicks links for your reference: