To enable data separation for a table, a sysdomain field must be added to its dictionary definition. This field is essential for the system to associate each record with a specific domain. The field must be a direct reference to the Domain [sysdomain] table. This reference relationship allows the platform to apply domain visibility rules, ensuring that users can only see records belonging to their own domain and any child domains. Using a reference field is the fundamental architectural requirement for the domain separation mechanism to function correctly.

A. A 'String' field type is incorrect because it cannot establish the required relational link to the sysdomain table, which is necessary for enforcing domain hierarchy and visibility rules.

C. While using the 'Domain ID' field type is a recommended shortcut that creates the correct reference, the fundamental requirement is the reference itself. Option B describes the underlying database structure, which is the core principle.

D. The field must be named sysdomain and must reference the Domain [sysdomain] table. Referencing the Company table is incorrect and would not enable domain separation.

1. ServiceNow Product Documentation: "Domain separate a table".

The documentation states, "Add a sysdomain field to the table dictionary entry... you can create a reference field that refers to the Domain [sysdomain] table." This confirms that the core requirement is a reference field named sysdomain pointing to the sysdomain table. (Accessed on various ServiceNow release documentation sites, e.g., Washington DC).

2. ServiceNow Training Courseware: "Domain Separation Implementation" On-Demand Course.

Module: "Domain Separating a Custom Application". The course material specifies: "To domain-separate a table, add a column to it named sysdomain. This column must be a reference to the Domain [sysdomain] table." This directly supports the answer by defining the essential field name and type.