Before you can create relationships in Networks Editor, a relationship class must exist between the feature class or table of the active feature and the feature class or table to relate. The relationship class determines which records can be related and whether the relationship is one-to-one, one-to-many, or many-to-many.

To configure relationships:

Configure relationships in the geodatabase, and publish the relationship classes as part of the feature service used by the application.

For information about configuring the origin and destination classes, relationship type, cardinality, and key fields, see Create Relationship Class in the ArcGIS Pro documentation.

You must use Global ID fields instead of Object ID fields as relationship keys so that Networks Editor can support relationships reliably.

There are certain predefined rules for every feature when it comes to creating a relationship between features, see Manage Relationship Class Rules.