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

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 can’t 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, there’s 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 Dollar’s 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 what’s desirable and what’s 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 reserve 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!

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