The identifier of the source DB instance from which to restore. Constraints: 
- Must be the identifier of an existing database instance
- Must contain from 1 to 63 alphanumeric characters or hyphens
- First character must be a letter
- Cannot end with a hyphen or contain two consecutive hyphens
 Declaration Syntax
 Declaration Syntax| C# | 
public string SourceDBInstanceIdentifier { get; set; }