How To Fix USMD1090 - Entity type &1, relationship &2: Leading entity type &3 is not unique

USMD1090 - Overview

• Message type: E = Error

• Message class: USMD1 - Datenmodel

• Message number: 090

• Message text: Entity type &1, relationship &2: Leading entity type &3 is not unique

What causes this issue?

The <LS>From-entity type </>&V4& has the leading entity type &V3&, which
needs to be unique in the context of the <LS>To-entity type </>&V1&:
&V3& must be either a part of the key of &V1& or must be assigned
through exactly one relationship of the type <LS>Referencing</> to the
entity type &V1&.

System Response

The data model cannot be activated.

How to fix this error?

Adjust the data model so that the condition described above is
fulfilled.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.

USMD1090 - Details

• The SAP error message USMD1090 typically occurs in the context of SAP Master Data Governance (MDG) when there is an issue with the uniqueness of the leading entity type in a relationship. This error indicates that the system has detected that the leading entity type specified in the relationship is not unique, which can lead to ambiguity in data processing.
  
  Cause:
  The error message USMD1090 is triggered when:
  
  Non-Unique Leading Entity: The leading entity type (e.g., a business partner, material, etc.) is not unique in the context of the relationship being defined. This means that there are multiple instances of the leading entity that could potentially relate to the same instance of the dependent entity.
  Incorrect Configuration: The configuration of the relationship in the data model may not be set up correctly, leading to multiple instances of the leading entity being associated with the same dependent entity.
  Data Integrity Issues: There may be data integrity