In Experience Data Model (XDM), a required field indicates that it must be supplied a valid value in order for a particular record or time-series event to be accepted during data ingestion. Common use cases for required fields include user identity information and timestamps.
When defining a new field in the Adobe Experience Platform user interface, you can set it as a required field by selecting the Required checkbox in the right rail. Select Apply to apply the change to the schema.
Once the field is applied, its path appears under Required fields in the left rail. If the field is nested, then any parent fields will also appear as required.
This guide covered how to define a required field in the the UI. See the overview on defining fields in the UI to learn how to define other XDM field types in the Schema Editor.