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University of Minnesota Digital Conservancy >
University Digital Conservancy Preservation Policy
The University Digital Conservancy is committed to providing long-term access to the digital works it contains, and adheres to digital preservation best practices to ensure data accessibility, fixity, and usability in perpetuity. Understanding that software, hardware, and format obsolescence is a complex issue with outcomes that are difficult to predict, the UDC uses digital preservation strategies designed to anticipate unknown changes in the technological environment. The University Digital Conservancy cannot promise the same support for digital objects in all formats, but will promise to make explicit the level of support it will provide for each file format MIME type deposited in the UDC, and will provide best practices guidance for contributors in selecting formats for inclusion in the UDC.
Contributors should understand that the level of preservation support provided for works is determined by the file format in which it is submitted.
The overarching goal of the Digital Conservancy's preservation program is to deliver long-term access to digital information. Access to the intellectual content of files is dependent on the maintained integrity and usability of digital items. The following principles illustrate the Digital Conservancy preservation objectives.
Stability
The University Digital Conservancy maintains fixity (bitstream integrity) for all digital objects submitted in the UDC. This is accomplished using a checksum algorithm (MD5) that verifies that the bitstream of a digital object matches its original bitstream (from date of original deposit in the UDC).
Accessibility
The University Digital Conservancy provides persistent access to all digital objects in the original formats in which they were submitted. This is accomplished through the use of persistent identifiers that point to the digital objects and/or their metadata. The UDC provides secure storage and backup services.
Usability
The University Digital Conservancy will take reasonable steps to ensure the usability of digital objects placed in its custody. Preservation steps include format migration, emulation, and normalization. Which steps the UDC will take to perpetuate usability of a file are determined by the nature of the file format. More extensive actions will be taken to preserve usability for objects in file formats that are fully disclosed, well documented, widely adopted, and are most accessible for migration, emulation, or normalization actions. Fewer actions will be taken to preserve usability for file formats that are proprietary and/or undocumented, and those that are considered working formats (e.g., Photoshop .psd) and/or are not widely adopted.
Digital Preservation Support Levels
| | Full Support
(level 1) | Limited Support
(level 2) | Minimal Support
(level 3) |
| Assigns a persistent identifier that will always point to the object and/or its metadata | • | • | • |
| Creates provenance records and other preservation metadata to support accessibility and management over time | • | • | • |
| Provides secure storage and backup | • | • | • |
| Performs periodic refreshment to new storage media | • | • | • |
| Performs routine fixity checks using proven checksum methods | • | • | • |
| Undertakes strategic monitoring of format | • | • |
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| Provides storage in a trusted preservable format (making a normalized version, if necessary) | • |
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| Plans and performs migration to succeeding format upon obsolescence | • |
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Full Support (level 1)
Will take all reasonable actions to maintain usability. Actions may include migration, emulation, or normalization. Will ensure access and data fixity.
Limited Support (level 2)
Will take limited steps to maintain usability. May actively transform a file from one format to another to mitigate format obsolescence. Will ensure access and data fixity.
Minimal Support (level 3)
Will provide for access to the item in its submission file format only. Will work to ensure data fixity (make sure the physical bitstream of the file does not change).
File Support and Preservation Best Practices
The following table details Digital Conservancy preservation support levels for commonly used file formats. Best practices for file formats are included.
| TEXT AND MICROSOFT OFFICE FILE FORMATS |
| Format |
File |
Support Level |
UDC Best Practices |
| HTML |
.html, .htm |
Level 2 |
Must include all other referenced files, including CSS files and any includes. |
| Microsoft Word |
.doc |
Level 2 |
Though acceptable for deposit, the UDC best practice is to convert to PDF prior to deposit. |
| Microsoft PowerPoint |
.ppt |
Level 2 |
Disable all macros and other effects. Conversion to PDF is also an excellent option. |
| Microsoft Excel |
.xls |
Level 2 |
Disable all macros. You may also wish to export dataset into a tab-delimited text file (.txt) prior to deposit. |
| PDF |
.pdf |
Level 1 |
PDF/A is the preferred version of PDF for archival preservation |
| Postscript |
.ps |
Level 2 |
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| Rich Text |
.rtf |
Level 2 |
For increased support, you may wish to consider conversion to PDF. |
| Plain Text |
.txt |
Level 1 |
It is recommended that all .txt files be saved using the UTF-8 (Unicode) character set. |
| SGML |
.sgm, .sgml |
Level 1 |
Requires that the depositor also include the DTD along with the SGML file. |
| XML |
.xml |
Level 1 |
To ensure the best available support, include the DTD along with the well-formed XML file. |
| IMAGE FILE FORMATS |
| Format |
File |
Support Level |
UDC Best Practices |
| BMP |
.bmp |
Level 3 |
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| GIF |
.gif |
Level 3 |
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| JPEG |
.jpg |
Level 1 |
When possible, save these files using no compression. |
| JPEG 2000 |
.jp2 |
Level 2 |
This file format holds much potential once tools and support become more widely available. Best practice is to save master files using no compression. |
| PNG |
.png |
Level 2 |
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| Photo CD |
.pcd |
Level 3 |
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| Photoshop |
.psd |
Level 3 |
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| TIFF |
.tif |
Level 1 |
Considered the best format for storing your master images. Best practice is to save these files with no compression. |
| AUDIO FILE FORMATS |
| Format |
File |
Support Level |
UDC Best Practices |
| MPEG audio |
.mp3 |
Level 2 |
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| Real Audio |
.ra, .rm, .ram |
Level 3 |
Proprietary format. It may be appropriate to convert to another format prior to deposit. |
| Wave |
.wav |
Level 1 |
The UDC recommends the use of this file format for capturing digital audio. This file format can store all the data in an uncompressed format and its wide use suggests long-term community support. |
| Windows Media Audio |
.wma |
Level 3 |
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Additional Information
Before beginning any imaging or audio project, you may wish to review the following documents. Each addresses current best practices in the area of digital imaging and digital audio creation.
Digital Imaging
California Digital Library
http://www.cdlib.org/inside/diglib/guidelines/bpgimages/cdl_gdi_v2.pdf
Collaborative Digitization Program
http://www.cdpheritage.org/digital/scanning/documents/WSDIBP_v1.pdf
Library of Congress
http://www.digitalpreservation.gov/formats/content/still_preferences.shtml
National Archives and Records Administration (NARA)
http://www.archives.gov/preservation/technical/guidelines.pdf
Digital Audio
Collaborative Digitization Program
http://www.cdpheritage.org/digital/audio/documents/CDP_DABPv2_1.pdf
University of Michigan
http://deepblue.lib.umich.edu/bitstream/2027.42/40248/1/Audio-Best_Practice.pdf
Go to the UDC home page
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