The REF database is required by Datical DB. 

REF Database in the Release Pipeline

REF is always the first step in a release pipeline. During packaging, SQL scripts are converted into changesets (deployable build artifacts) and deployed to the REF database. During deployment of the changes, Datical DB performs error-checking and rules validation (for rules configured for the project). 

You then use deploy operations to propagate database changes through the managed databases in the release pipeline. 

REF Database Permissions

The Datical DB user for the REF database requires additional permissions. 

In addition to the permissions for managed databases, it needs permissions to back up and restore the database. Packaging operations back up and restore the REF database as they profile and simulate the schema changes represented in the SQL files being packaged. 

The database-specific permissions needed are documented for each database type in Managed Databases.  

Initialization

Initialize the REF database after the project has been created. The project represents the release pipeline. 

Depending on your needs, you may choose to initialize the REF database in different ways. 

It should be a minimal, skeletal representation of the database. It may include stored logic and application data (DML) but not operational data. 

See Initializing the Reference Database (REFDB).