Library Digital Repository (LDR): Policy Overview

The University of Chicago Library Digital Repository (LDR) is a preservation repository of digital content for which the University of Chicago Library has assumed curatorial responsibility. It consists of both born-digital and retrospectively digitized materials. Its primary purpose is to ensure that this content persists through time.

Persistence in a digital context requires transformation of deposited content into new digital formats in cases where the originally deposited formats are at risk of becoming obsolete in time. The core responsibility of digital repository management is to ensure both physical and logical persistence. Ensuring persistence requires that bitstreams are kept physically intact, verifying that the bits have not been changed, corrupted or destroyed, and that they are logically readable, representing usable information by hardware and software that wants to consume the bitstreams and render them meaningfully.

The University of Chicago Library Digital Repository (LDR) is managed by the Digital Library Development Center in conjunction with the Special Collections Research Center, which includes the University Archives, and in consultation with the Preservation Department, to ensure that digital, archival and preservation best practices are applied. All three units are part of the University Library.

The LDR consists of two synchronized computer systems, each in a different physical location, on different hardware, each with RAID 6 storage. Content is copied nightly from the primary system onto the secondary system, which can also serve as a live copy of the first if needed. Content is transferred from the secondary system to the University of Chicago's central tape-storage system in yet another physical location. This provides disaster recovery, since tapes are rotated off-site. The method of copying from one system to another (rsync) ensures that all three copies of the LDR are identical. The same process is used when it is necessary to upgrade repository hardware by transferring files to new media or new systems. Each copy of the LDR contains all files as well as associated descriptive, administrative, technical, structural, and rights and permissions metadata.

When content is deposited into the LDR, it is inspected for at-risk digital formats (formats that are currently expected to become obsolete); if detected, content in these formats is preserved in the deposited formats but also converted into formats that are expected to persist for the foreseeable future. Format information is recorded in the events database, making it possible to use the database to monitor formats which may become at risk in future. Technical metadata is generated using standard tools and recorded upon deposit.

Checksums for each file are recorded using the MD5 and SHA-256 algorithms. Checksums are periodically generated for files on disk and compared against the recorded values. These checks are in addition to the verifications which the hardware and the system administrators routinely perform. All required PREMIS 3.0 data elements are recorded. (http://www.loc.gov/standards/premis/v3/)

The LDR supports discovery of the materials it contains by means of digital collections built from those materials and the descriptive records pointing to them. Descriptive metadata for these collections are available via the OAI-PMH protocol (http://www.openarchives.org/pmh/). Access to contents in the LDR is provided by means of linked data exposed via the SPARQL protocol (https://www.w3.org/TR/2013/REC-sparql11-protocol-20130321/).