The identifier for the source DB snapshot. Constraints: 
- Must specify a valid system snapshot in the "available" state.
- If the source snapshot is in the same region as the copy, specify a valid DB snapshot identifier.
- If the source snapshot is in a different region than the copy, specify valid DB snapshot ARN. For more information, go to Copying a DB Snapshot.
 Declaration Syntax
 Declaration Syntax| C# | 
public string SourceDBSnapshotIdentifier { get; set; }