The Migration of Optical Discs Book Supplements at the National Diet Library, Japan

The National Diet Library (NDL), as the only legal deposit library in Japan, is responsible for preserving its collections as cultural properties of the nation and passing them on to future generations. Regarding digital materials, the NDL has formulated the “Basic Plan for Digital Preservation of National Diet Library’s Collections for 2021-2025” and has been working on research and practice for digital preservation. The NDL is currently digitizing and migrating its collections, and as part of this process, a large-scale migration of about 10,000 optical discs was conducted in FY2023.
The migration mainly targeted CDs of book supplements published in Japan up to the year 2000. The types of discs were diverse and included CD-ROMs that simply stored a few files, audio CDs, hybrid CDs, and relatively early DVD-Video (DVD players began to be produced in 1996), as well as optical discs containing large numbers of files with programs like databases.
In order to migrate these diverse discs efficiently, we designed a workflow that classifies discs in advance and extracts data in a manner appropriate for each type of disc format. Optical discs were classified into three main categories: optical discs for simply copying files, for extracting audio tracks only, and for imaging in ISO format. It was confirmed that the method of imaging everything regardless of disc’s type was the most efficient for migration work, although there were many technical issues in searching and using the contents of image files.
In addition, in this work, all optical discs were subjected to an error check equivalent to ISO/IEC 18630:2023 before the data extraction. As a result, it was confirmed that, especially for audio CDs, there was a correlation between high error values and noise in the migration results. Therefore, we found that the appropriate use of error check can improve the efficiency of quality inspection of audio CD migration.
In this poster, we will report on the issues and propose an efficient technical method for the migration of various optical discs published more than a quarter of a century ago.