primary identity in Real-Time Customer Profile and identity graph

[cfreely]

There is a note in this document:

A single schema may have many identity fields defined, but can only have one primary identity. All identity fields (primary or otherwise) contribute to the identity graph for an individual customer, but Real-Time Customer Profile uses only the primary identity as the source of truth when merging data fragments together. If you want to enable a schema for use in Profile, the schema must have a primary identity defined.

I didn't understand this note. Isn't the profile merge of the Real Time Customer Profile built based on the identity graph? Why do these non primary identities only participate in the identity graph but do not affect the profile merge?

Regards

[birthariyamayank]

Hi,

Experience league document explains it well: 

Each customer profile is composed of multiple profile fragments that have been merged to form a single view of that customer. For example, if a customer interacts with your brand across several channels, your organization will have multiple profile fragments related to that single customer appearing in multiple datasets. When these fragments are ingested into Platform, they are merged together in order to create a single profile for that customer.

In other words, profile fragments represent a unique primary identity and the corresponding record or event data for that ID within a given dataset.

When the data from multiple datasets conflicts (for example one fragment lists the customer as “single” while the other lists the customer as “married”) the  merge policy determines which information to prioritize and include in the profile for the individual. Therefore, the total number of profile fragments within Platform is likely to always be higher than the total number of merged profiles, as each profile is typically composed of multiple fragments from multiple datasets.

[cfreely]

Thanks @birthariyamayank !

In this way, I understand that only primary identity will work in profile merge, so does identity graph have any practical effect? Especially in the segmentation service.

Regards

[birthariyamayank · Accepted solution]

Yes, AEP uses deterministic Identity resolution, which will link different IDs having a common ID (regardless of Primary & Non-Primary), which may lead to a scenario where Profiles will collapse (the shared device is a classic example), which will eventually have an impact on segmentation.