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Digital Preservation Policy

For the purpose of this policy, preservation will include any activity with managerial and financial considerations with the purpose of ensuring access to digital material under the care of the Northwestern University Libraries’ Digital Repositories for a period of time determined by striking a balance between the needs of users and the priorities of Northwestern University Libraries. These activities include, but are not limited to, provision of repository services, storage, policy development, and methods involved in preserving digital items and the information contained in those items.

The Northwestern University Libraries’ Digital Preservation Policy outlines a plan to support sustainable access to select digital collection content for the foreseeable future. This policy is subject to change as new and emerging technologies impact the ability to preserve digital content.

Policy Statement

The Northwestern University Libraries follows a policy of active preservation with the aim of ensuring the authenticity, reliability, and integrity of the digital collection assets entrusted to and under their care, while attempting to provide usable versions for research, teaching, and learning.

Contextual Policies

Northwestern University Libraries’ Digital Preservation Policy should be approached in the context of other existing university, library, and repository policies, including the Collection Development Policy, Use of Electronic Resources, Rights and Permissions, NU Network Privacy, and other related policies that may be developed in the future.

Identification of Content

The preservation of items in Northwestern University Libraries’ digital repositories is key to the Libraries’ mission “to provide collections and information services of the highest quality to sustain and enhance the University’s teaching, research, professional and performance programs.”

The general scope of this policy covers digital items created by Northwestern University Libraries, digital materials that comprise the university scholarly record, and preservation master digital surrogates of physical library collection material. More specifically, this includes:

Preservation Objectives

Northwestern University Libraries seeks to provide its stakeholders long-term access to usable versions of the digital material entrusted to its care to the best of its ability.

Some basic preservation support services we provide for all items in the repository include:

Auditing

As part of a digital preservation process, it is important to check data integrity on a regular basis. A set of automated processes will perform an audit on the data continually, including looking for corruption, content model and metadata correctness, missing data, and more. The use of automation is to remove the human element as much as possible (including errors as well as person-hours required) and generate regular status reports where staff action can be taken when a problem is found. A continually-running, ongoing (rather than a yearly) process can help catch issues more quickly, and can better help balance system resources as some elements of the audit process can take a long time and use network and CPU resources.

Dark Archive Services

In some cases content has significant replacement cost, or is of extremely high importance. The archival copies of this content will be stored in an additional archival system (such as DPN, Chronopolis, APTrust, or DuraCloud) as a further precaution to ensure that the content remains stable over a long period of time. These storage systems store the content in geographically disparate areas on multiple architectures as a dark archive where content isn't touchable or seen (except when restoration is needed). As new content is ingested into the repository, future workflows will allow Library staff to flag content if it needs this added layer of preservation.

Due to limited library resources and/or the nature of digital file formats themselves, not all formats will be fully supported by Northwestern University Libraries for long-term preservation. Over time, digital files placed in the care of Northwestern University Libraries are preserved as is, transformed to new formats, or migrated to new platforms depending on the level of support designated for a particular format. Materials in formats determined by library staff to be out of scope will be purged or receive only basic preservation support. For more details, see: File Format Recommendations for Long-Term Preservation

Levels of Preservation Support

Level 1

Description:
Highest level of preservation support pledges Northwestern University Libraries best effort to maintain viability (integrity of the file), renderability (ability to display the file for viewing), and understandability (the file is displayed in a manner that does not affect the viewer’s ability to understand the file contents), as well as functionality of original digital object.

Criteria of file to ensure Level 1 support :

  • Is in a format that is publicly documented (example: wav);
  • Is in a format that is widely adopted (example: pdf);
  • Is in a format that may be rendered by multiple software packages (example: txt);
  • Is in a format that has lossless data compression (example: uncompressed tiff files); and
  • Contains no embedded files or dynamic content (example: txt).

Actions:

  • Monitor file format for changes that might warrant transformation or reassessment;
  • Migration of file to successive format when necessary (most likely due to format obsolescence);
  • Proprietary formats present challenges to some preservation activities. When possible, widely-used and supported formats such as pdf files will be transformed to a format that preserves the content and when possible the formatting and style of the original, but not necessarily the functionality.
  • Basic preservation including:
    • bitstream maintenance;
    • persistent, permanent identifier;
    • preservation metadata;
    • onsite and offsite backup copies;
    • regular virus and file corruption checks; and o periodic refreshments to new storage media.

Examples of supported file types:

  • UTF-8 Unicode text (.txt) – plain text document in Unicode
  • PDF/A – Adobe PDF
  • TIFF 24-bit, uncompressed (.tif, .tiff)–uncompressed images
  • WAV (PCM) (.wav) – uncompressed audio

Level 2

Description:

Mid level of preservation support pledges Northwestern University Libraries’ best effort to maintain viability (integrity of the file), and understandability (the file is displayed in a manner that does not affect the viewer’s ability to understand the file contents). Files of this type will not be migrated to successive formats nor updated to new standards. For example, .html files written in HTML4 will not be migrated to HTML5. For compound files determined to be of high value, Level 1 support could be offered to individual components of that file. For example, a high value MP4 would receive Level 2 support, but its individual streams (AAC audio, H.264 video, SRT/TXT captions, artwork, metadata) could be pulled out and converted to a format that can be preserved at Level 1.

Criteria of file to ensure Level 2 support:

  • Is in a format that is publicly documented (example: xml file in MODS);
  • Is in a format that is widely adopted (example: .mp3);
  • Is in a format that may be rendered by multiple software packages (example: .csv);
  • May be in a format with lossy data compression (example: jpg); and/or
  • Is in a format that does not meet the criteria for Level 1.

Actions:

  • Monitor file format for changes that might warrant reassessment to Level 1 or 3;
  • Rendered formats (such as .html and other markup languages) present challenges with newer versions of rendering software. These formats will not be transformed to newer versions but the content will be wholly preserved.
  • Container formats (such as .avi and .ogg) present challenges as the files that make up the final file can fall out of use even though the format itself is still in use, so that an avi file does not play on a video player that plays other avi files flawlessly due to contained file issues. When possible, these files will be transformed to a format that preserves as much content as is possible on a case-by-case basis.
  • Basic preservation including:
    • bitstream maintenance;
    • persistent, permanent identifier;
    • preservation metadata;
    • onsite and offsite backup copies;
    • regular virus and file corruption checks; and o periodic refreshments to new storage media.

Examples of content-only-supported file types:

Level 3

Description:

Basic level of preservation support pledges Northwestern University Libraries’ best effort to maintain viability (integrity of the file) of original digital object only.

Criteria of file to ensure Level 3 support:

Actions:

Only basic preservation of original object including:

Examples of basic-supported file formats:

Preservation Action Level 1 Level 2 Level 3
Provision of persistent identifier for object and/or its metadata (for items in the Institutional Repository only)  X X X
Creation of preservation metadata X X X
Secure storange and backup X X X
Regular fixity checks X X X
Regular virus checks X X X
Periodic refreshment to new storage media X X X
Storage of original digital object X X X
Strategic monitoring of format for changes X X
Migration to successive format upon obsolescence X
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