Encapsulation
Encapsulation in the context of preserving digital materials is a technique of grouping together a digital object and anything else necessary to provide access to that object. This technique aims to overcome the problems of the technological obsolescence of file formats because the details of how to interpret the digital bits in the object can be part of the encapsulated information. Encapsulation can be achieved by using physical or logical structures called "containers" or "wrappers" to provide a relationship between all information components, such as the digital object and other supporting information such as a persistent identifier, metadata, software specifications for emulation.
The encapsulation may be composed of analogue and digital components. An example of an analogue component would be human readable instructions, such as writing on the outer case of a physical format carrier, to describe how to use the carrier and interpret the outer most layer of the digital component, most likely the wrapper, which will in turn provide the information required to use the rest of the digital information contained. The analogue component of the encapsulated object may change as the carrier needs to be refreshed but ideally there should be no change required of the digital component when it is stored this way.
The types of supporting information that should be included in an encapsulation, apart from the digital object itself, are described by the Reference Model for an Open Archival Information System (OAIS) which are based on the report "Preserving Digital Information" from the Task Force on Archiving of Digital Information. Briefly, they are: the representation information used to interpret the bits appropriately for access; the provenance to describe the source of the object; the context to describe how the object relates to other information outside the container; reference to provide one or more identifiers to uniquely identify the object; and fixity to provide evidence that the object has not been altered.
An alternative to storing the representation information to decode the bit-stream with every digital item archived, is to include a pointer to a single storage area for that information. This could be stored in the same repository or another dedicated centralised repository.
Research Overview
The concept of encapsulation is similar to the "bento container" developed in 1993 by Apple computers to increase compatibility of data between computer applications. Bento (PDF file) is a specification for storage and interchange of compound content, and is designed to be platform and content neutral, so that it provides a convenient container for transporting any type of compound content between multiple platforms.
More recently, encapsulation has been widely promoted by Jeff Rothenberg in a number of his published materials (such as Chapter 9. Research Required for the Emulation Approach in "Avoiding Technological Quicksand", specifically 9.3 Encapsulation techniques). Rothenberg is a strong advocate of encapsulation and emulation methods for digital preservation. The encapsulation approach has been supported by others such as Michael Day of CEDARS (Metadata for Preservation CEDARS Project Document AIW01 and Issues and Approaches to Preservation Metadata (also available from RLG/NPO conference "Guidelines for Digital Imaging" proceedings)) and Tom Shepard of UPF (Universal Preservation Format (UPF): Conceptual Framework RLG Diginews, vol 2 no 6, Dec 15 1998).
David Bearman disputes Rothenberg's theory in Reality and Chimeras in the Preservation of Electronic Records stating that it is not clear enough yet how metadata encapsulation strategies may be practically implemented.
The Universal Preservation Format (UPF) is a method being developed for digital preservation, based on the theory of encapsulation. It is a "self-describing" storage technology which uses a wrapper to hold the essence (the digital object) and the metadata together to protect against technological obsolescence.
The Reference Model for an Open Archival Information System (OAIS) p.17-19, also describes a method of encapsulation in describing the concept of an "information package" (IP) which is "content information" and "preservation description information" contained by "packaging information".
The Digital Rosetta Stone is a method of storing the representation information needed to interpret the digital content of an object separate from the encapsulation to avoid duplication of effort and inefficient use of storage space.
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Avoiding Technological Quicksand : Finding a Viable Technical Foundation for Digital Preservation
Rothenberg, Jeff
In: CLIR Reports
(Date Created: 15 Jan 1998)
Reviewed by: Reality and Chimeras in the Preservation of Electronic Records
- This report to the Council on Library and Information Resources discusses digital preservation strategies and recommends emulation as the best possible solution to the digital preservation challenge. Rothenberg advocates the development of specifications to build an emulator for a digital document and its associated software, which are stored with the document. The work of building the emulator is not done until the document needs to be accessed.
- http://www.clir.org/pubs/reports/rothenberg/contents.html
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Beyond Migration: Preserving Electronic Documents with Digital Tablets
Kranch, Douglas A.
(Date Created: Sep 1999)
- This paper discusses the need for digital preservation and predicts how it could be accomplished with future stable technologies which will encapsulate the hardware, software and data in the form of electronic tablets.
- ISSN: 0730-9295
- Information Technology and Libraries, September 1998, pp. 138-148
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Carrying Authentic, Understandable and Usable Digital Records Through Time
Bikson, T.; RAND-Europe; Rothenberg, J.
(Date Created: 6 Aug 1999)
- This report to the Dutch National Archives and Ministry of the Interior presents the results of a study to define a strategy and framework for the long-term management and preservation of digital governmental records. A "testbed" in which specific digital preservation techniques can be prototyped and evaluated is proposed.
- http://www.digitaleduurzaamheid.nl/bibliotheek/docs/final-report_4.pdf
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Collection-Based Persistent Digital Archives - Part 1
Baru, Chaitan; Gupta, Amarnath; Ludaescher, Bertram; Marciano, Richard; Moore, Reagan; Rajasekar, Arcot; San Diego Supercomputer Center; Schroeder, Wayne; Wan, Michael
In: D-Lib magazine
(Date Created: Mar 2000)
- This article, from the San Diego Supercomputer Center, "defines an approach for maintaining digital data for hundreds of years through development of an environment that supports migration of collections onto new software systems." "The ultimate goal is to preserve not only the bits associated with the original data, but also the context that permits the data to be interpreted." See also Part 2 of this article which describes the creation of a one million message persistent email collection.
- http://www.dlib.org/dlib/march00/moore/03moore-pt1.html
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Collection-Based Persistent Digital Archives - Part 2
Baru, Chaitan; Gupta, Amarnath; Ludaescher, Bertram; Marciano, Richard; Moore, Reagan; Rajasekar, Arcot; San Diego Supercomputer Center; Schroeder, Wayne; Wan, Michael
In: D-Lib magazine
(Date Created: Apr 2000)
- This article, from the San Diego Supercomputer Center, describes a project to create a one million message persistent email collection. Following on from Part 1 , which describes the development of an environment that supports migration of collections onto new software systems, this article discusses the four parts of a persistent archive system: "support for ingestion, archival storage, information discovery, and presentation of the collection."
- http://www.dlib.org/dlib/april00/moore/04moore-pt2.html
- In D-Lib Magazine, Vol 6, No. 4
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Digital Rosetta Stone: A Conceptual Model for Maintaining Long-term Access to Digital Documents
Heminger, Alan R.; Robertson, Steven B.
(Date Created: 17 Jun 1998)
- This document describes a method for digital preservation relying on keeping a "meta-knowledge archive" of how to interpret media formats and file formats to support data recovery and document reconstruction processes.
- http://www.ercim.org/publication/ws-proceedings/DELOS6/rosetta.pdf
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Issues and Approaches to Preservation Metadata
Day, Michael; UKOLN
(Last Updated: 24 Feb 1999)
- The creation and use of metadata is likely to become an important part of all digital preservation strategies whether they are based on hardware and software conservation, emulation or migration. The UK Cedars project aims to promote awareness of the importance of digital preservation, to produce strategic frameworks for digital collection management policies and to promote methods appropriate for long-term preservation - including the creation of appropriate metadata.
- http://www.ukoln.ac.uk/metadata/presentations/rlg-npo/warwick.html
- also at: http://www.ukoln.ac.uk/metadata/presentations/rlg-npo/warwick.html
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Metadata for Preservation : CEDARS Project Document AIW01
Day, Michael
In: Cedars : Curl Exemplars in Digital Archives Project
(Last Updated: 3 Aug 1998)
(United Kingdom)
- This report is a review of metadata formats and initiatives in the area of digital preservation. It supplements the DESIRE Review of metadata (Dempsey et al. 1997). It is based on a literature review and information derived from a number of workshops.
- http://www.ukoln.ac.uk/metadata/cedars/AIW01.html
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Metadata to Support Data Quality and Longevity
Rothenberg, Jeff
(Last Updated: 3 Jun 1996)
- This paper discusses two key needs for metadata: to support data quality and to ensure the longevity of data. In the latter category, the need for encapsulation with metadata which will enable future emulation is discussed.
- http://web.archive.org/web/20040727082521/http://www.computer.org/conf
erences/meta96/rothenberg_paper/ieee.data-quality.html
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Reality and Chimeras in the Preservation of Electronic Records
Bearman, David
In: D-Lib magazine
(Date Created: 15 Apr 1999)
- This magazine column is a response to the report to CLIR by Jeff Rothenberg "Avoiding Technological Quicksand". Bearman gives a critique of the solution described by Rothenberg and suggests that migration is still the preferred solution for the preservation of electronic records.
- http://www.dlib.org/dlib/april99/bearman/04bearman.html
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Reference Model for an Open Archival Information System (OAIS)
Consultative Committee for Space Data Systems (CCSDS)
(Regularly Updated)
- Developed by the CCSDS, OAIS is a model for an archival system for the long-term preservation of and access to digital information. The reference model is now an ISO standard (ISO 14721). This site provides access to the final blue book CCSDS 650.0B-1 version of the standard.
- http://public.ccsds.org/publications/archive/650x0b1.pdf
- All drafts available from http://ssdoo.gsfc.nasa.gov/nost/isoas/ref_model.html
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State of the Art and Practice in Digital Preservation
Lee, Kyong-Ho ; Lu, Richang ; McCrary, Victor ; Slattery, Oliver ; Tang, Xiao
(Date Created: Jan 2002)
- This paper published in the Journal of Research of the National Institute of Standards and Technology (vol. 107, no. 1, pp. 93-106, Jan-Feb 2002) is a survey of ideas and practice in digital preservation as of late 2001. It first elaborates the various proposed strategies for digital preservation (including emulation and migration) before introducing a number of projects from Australia, Europe and North America. A final section recommends the development of preservation standards based on XML, and outlines some critical issues that still need to be resolved.
- http://nvl.nist.gov/pub/nistpubs/jres/107/1/j71lee.pdf
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Trustworthy 100-Year Digital Objects : Evidence Even After Every Witness is Dead
Gladney, H. M.
(Date Created: May 2003)
- Unpublished discussion paper (43 pages) by Dr Gladney which was later rewritten. This paper considers how publishers can guarantee the long-term authenticity of electronic papers.
- http://eprints.erpanet.org/archive/00000008/
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XML and Digital Preservation
Testbed Digitale Bewaring
(Date Created: Sep 2002)
(Netherlands)
- This paper describes XML and how it is useful for preserving digital information. A summary of current knowledge and research into XML is also provided.
- http://www.digitaleduurzaamheid.nl/bibliotheek/docs/white-paper_xml-en
.pdf
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Bento Specification, Revision 1.0d5
Apple Computer Inc.; Harris, Jed; Ruben, Ira
(Date Created: 15 Jul 1993)
- This specification (106 p.) defines the format of data in a Bento container, and an API for writing and reading Bento containers. Bento containers are used by application programs to store compound content that consists of multiple content objects.
- http://info.wgbh.org/upf/pdfs/BentoSpec1_0d5.pdf
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Policies, Strategies & Guidelines
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Cedars Guide To: Digital Preservation Strategies
University of Leeds
(Last Updated: 02 Apr 2002)
(United Kingdom)
- This guide includes recommendations about technical approaches to digital preservation based on the Cedars experience.
- http://www.leeds.ac.uk/cedars/guideto/dpstrategies/
- ISO Archiving Standards : Overview
NASA
(Regularly Updated)
- This site contains links and background information to the Reference Model for an Open Archival Information System (OAIS) and other archival standardization efforts.
- http://ssdoo.gsfc.nasa.gov/nost/isoas/overview.html
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Projects and Case Studies
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UPF (Universal Preservation Format) Home Page
UPF, WGBH
(Last Updated: 1998)
(United States of America)
- Sponsored by the WGBH Educational Foundation and funded in part by a grant from the National Historical Publications and Records Commission of the National Archives, the Universal Preservation Format initiative advocates a platform-independent format that will help make accessible a wide range of data types. The UPF is characterized as "self-described" because it includes, within its metadata, all the technical specifications required to build and rebuild appropriate media browsers to access contained materials throughout time. The project has produced a Recommended Practices document.
- http://info.wgbh.org/upf/
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Victorian Electronic Records Strategy Final Report
Public Records Office, Victoria
(Last Updated: 31 Mar 1999)
(Australia)
- The Victorian Electronic Records Strategy (VERS) Project was undertaken by Public Record Office Victoria (PROV) in conjunction with the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Ernst & Young from April to December 1998. The project aimed to demonstrate the feasibility of capturing and preserving electronic records in such a way that they may be readily accessed in the long term; and to provide a set of functional descriptions for electronic archiving which can be used by Victorian government agencies to implement electronic archiving systems and strategies. The final report includes functional descriptions and a general description of the demonstrator system.
- http://www.prov.vic.gov.au/vers/pdf/final.pdf
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Reference Model for an Open Archival Information System (OAIS)
Consultative Committee for Space Data Systems (CCSDS)
(Regularly Updated)
- Developed by the CCSDS, OAIS is a model for an archival system for the long-term preservation of and access to digital information. The reference model is now an ISO standard (ISO 14721). This site provides access to the final blue book CCSDS 650.0B-1 version of the standard.
- http://public.ccsds.org/publications/archive/650x0b1.pdf
- All drafts available from http://ssdoo.gsfc.nasa.gov/nost/isoas/ref_model.html
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Related Topics: Emulation | Migration
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Digital preservation strategies
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