Emulation, Migration and Long-Term Preservation of Electronic Records

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Emulation, Migration and Long-Term Preservation
of Electronic Records

• Cal Lee
• University of Michigan
• School of Information
• ECURE 2001 Preservation and Access for
  Electronic College and University Records
• October 13, 2001

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Outline

• The Digital Preservation Problem
• Base-Line Assumptions
• Major Approaches Migration and Emulation
• Migration
• Emulation
• For Further Reference

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The Digital Preservation Problem
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Technological Dependency

• Digital objects are useless if we cant interact
  with them
• Those interactions depend on numerous technical
  components.

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Key Concept - Abstraction

• "Computer science is largely a matter of
  abstraction identifying a wide range of
  applications that include some overlapping
  functionality, and then working to abstract out
  that shared functionality into a distinct service
  layer (or module, or language, or whatever).
  That new service layer then becomes a platform on
  top of which many other functionalities can be
  built that had previously been impractical or
  even unimagined. How does this activity of
  abstraction work as a practical matter? It's
  technical work, of course, but it's also social
  work. It is unlikely that any one computer
  scientist will be an expert in every one of the
  important applications areas that may benefit
  from the abstract service. So collaboration will
  be required. (emphasis added) - Phil Agre,
  Red Rock Eater, March 25, 2000

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Oh so many layers

• Physical medium - only layer yielding real
  consensus
• Bit
• Byte
• Character encoding
• Instruction set architecture
• Physical organization of bytes
• Logical organization of chunks
• Reading hardware
• Input/output hardware
• Input/output software

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But, wait, theres more

• Operating system kernel
• Network operating system
• Networking protocols
• Desktop and windowing environment
• Data syntax
• Data structure
• Data semantics
• Data content
• Data values
• Contextual linking within and between objects

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Obsolescence

• "Those who forget the past are condemned to
  reload it."
• - Nick Montfort, July 2000
• All layers undergo change over time, at varying
  rates.

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Some Base-Line Assumptions

• Several assumptions which I will take to be
  given.
• Making them explicit can help us to be more
  precise about available options and their
  costs/benefits.

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Assumption 1 Digital objects are instructions
for future interaction

• Only a small part of preservation work is about
  treating them like physical artifacts.
• Jeff Rothenberg takes this even farther,
  contending that all digital objects should be
  seen as programs.

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Assumption 2 Bits will be Bits

• Bit rot and advantages of newer media both call
  for periodic refresh and reformatting.
• Ensuring the integrity of the bit stream in such
  transfers is extremely important.
• See Charles Dollars 1999 book for an excellent
  explanation of these processes.

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Assumption 3 Change Happens

• Any long-term strategy must recognize that any
  underlying technical platform will eventually be
  abandoned by the industry and thereafter
  increasingly difficult to support.
• Ongoing preservation effort is assumed,
  regardless of the strategy adopted.
• Goal is to minimize (rather than eliminate) work
  and maximize the benefits.

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Assumption 4 Must identify whats desirable and
whats possible

• Best, most informed guess about how objects will
  be used.
• Characteristics that support such use.
• Currently available technical approaches.
• Whether using any given approach can
  cost-effectively preserve those characteristics.
• All of these decisions should be well documented
  and revisited periodically.

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Major Approaches Migration and Emulation
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Migration

• Periodic transformation of the bits/bytes to run
  directly on newer platforms.
• Used widely as an approach to actively managing
  legacy systems.
• Work can be expensive and introduce errors of
  translation.
• Since the resulting objects can run directly on
  newer platforms, layers of technology can be
  minimized.

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Emulation - Oxford English Dictionary, Second
Edition

• To reproduce the action of or behave like (a
  different type of computer) with the aid of
  hardware or software designed to effect this to
  run (a program, etc., written for another type of
  computer) by this means.

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Popular Examples from the History of Emulation

• Hardware and software - IBM System/360 (1963)
• Operating systems
• IBM MVS (1972)
• Amiga (1985)
• Microsoft Z80 Softcard (1989)
• DOS emulation in Windows (1987)
• SoftWindows (for Macintosh)
• Virtual PC (1997)
• Wine (Windows Emulator, 1993)

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More Emulation Examples

• Processors - Intel 8080 (1974)
• Virtual Machines - Java (1995)
• Terminal emulators - Telnet (1969), WinFrame
  (1995)
• Lots and lots of games

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Broad Issues to Address

• What level to emulate
• When to create the emulator - now vs. later, once
  vs. periodically
• How to develop emulators - what language, what
  platform
• Intellectual property rights

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Arguments for preservation using emulation

• Rothenberg - specification, interpreter, virtual
  machine
• IBM - distinction between preserving data files
  and programs, create emulators to run on
  Universal Virtual Computer (UVC)
• CEDARS - maintain byte stream, focus on
  preserving the significant properties of its
  underlying abstract form (UAF)
• CAMiLEON - create emulator in a (simplified)
  high-level language, migrate emulator across
  platforms when necessary

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Critiques of Emulation

• David Bearman most vocal critic
• Metadata and functional requirements are what
  counts for preserving electronic records
• Emulation attempts to capture too much (full
  functionality of technical environment) and not
  enough (essential characteristics of records)

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A Balanced Perspective on Preservation Strategies

• No single solution
• Identify requirements THEN evaluate the technical
  options.
• What attributes should be preserved (which
  differences matter)?
• Make (and document) educated guesses of costs and
  benefits.

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For Further Reference

• Growing literature on these issues
• Several prominent projects now and in recent
  years
• Please see the bibliography associated with this
  presentation

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Thank you!