By Adrian Turner, CDL Data Acquisitions consultant

The "CDL Guidelines for Digital Objects, Version 2.0" (CDL GDO) has been updated to reflect modified requirements for METS unique identifiers.  You can find the updated version at .

The revision applies to Section 3.1 only, and pertains to objects submitted for the CDL’s "Enhanced Service Level”.  This service level encompasses the presentation of digital assets via CDL websites. It is also sufficient for increased preservation services in the UC Libraries Digital Preservation Repository.

The METS top-level <mets> tag must contain an OBJID attribute containing an ARK identifier for the digital object.  Previously, the CDL GDO indicated that the OBJID attribute could contain a unique local identifier in lieu of an ARK identifier.  CDL systems do not support this scenario, however, for objects submitted for the Enhanced Service Level only.

Please contact the CDL at Digital Special Collections ( if you have any questions.