Mind the (Intelligibility) Gap

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Mind the (Intelligibility) Gap Yannis Tzitzikas, Giorgos Flouris Institute of Computer Science FORTH {tzitzik,fgeo}@ics.forth.gr

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Mind the (Intelligibility) Gap. Yannis Tzitzikas, Giorgos Flouris Institute of Computer Science FORTH {tzitzik,fgeo}@ics.forth.gr. Introduction on Dependencies. - PowerPoint PPT Presentation

Transcript of Mind the (Intelligibility) Gap

Page 1: Mind the (Intelligibility) Gap

Mind the (Intelligibility) Gap

Yannis Tzitzikas, Giorgos Flouris

Institute of Computer ScienceFORTH

{tzitzik,fgeo}@ics.forth.gr

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Introduction on Dependencies

• Dependencies: a set of requirements (prerequisites) for something to be useful (readable, understandable, viewable, executable, …)

• Dependencies of this presentation:– Powerpoint software– Computer system, properly setup – Overhead projector– Knowledge of English language– …

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Motivation

• Our purpose:– To model the dependencies of digital objects

• Problem of preservation– Maintain a digital object in a usable state in the future– Must have access to all the modules (e.g., software,

hardware, tacit or external knowledge etc) that it depends on

• A dependency model could help in determining:– Usability– What is missing to become usable– Necessary actions when something is about to become

unusable (e.g., a depending module becomes obsolete)

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Modules and Dependencies

• Dependencies– A set of requirements for something to be useful– C depends on D (C>D) if C cannot be used (read,

understood, viewed, executed, …) without D

• A dependency relation applies between modules– Any physical or non-physical object can be a module

• Module types:– Software, hardware, explicit or tacit knowledge, mental or

physical abilities, documentation, manuals, …– Digital objects are special types of modules

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Wordpad software

ORNotepad software

Modeling Example

readme.txt

Wordpad software

computer system

Greek language

power outlet

Windows software

Monitor

Notepad software

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Dependency Graphs

{A}

{B,C}

{E}

{D}

{C}

{B}

A depends on E {A}>{E}A depends on B or C {A}>{B,C}D depends on B or C {D}>{B,C}B depends on D {B}>{D}D depends on F {D}>{F}F depends on B {F}>{B}

{F}

{G}

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Preservation System

Preservation Setting

DependencyGraph

A A AA D E

F

System Profile: TS

C F

User Profile: Tu

D

All interesting modules are modeled here

{A}

{B,C}

{E}

{D}

{C}

{B} {F}

{G}

{A}

{B,C}

{E}

{D}

{C}

{B} {F}

{G}

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Intelligibility Issues

E directly depends on D and G

E is intelligible if D and G are intelligible

E depends on E, D, G, {B,C}, B, F

E is intelligible if E, D, G, {B,C}, B, F are accessible

Tu1={D, F, G}

Tu1 is not self-intelligible (e.g., F is not intelligible)

Tu2={B, D, F, G}: self-intelligible

E is intelligible by Tu2

E is not intelligible by Tu1

Missing module: B (Intelligibility Gap)

{A}

{B,C}

{E}

{D}

{C}

{B} {F}

{G}

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Emulators (Migrators, Translators, …)

A B

E

{A}

{C,E} {C,B}

Not in profile

Unintelligible

{C}

To read a postscript (ps) file without access to a postscript reader, one can transform it into pdf (using ps2pdf.exe), then read it using Acrobat Reader

readme.ps readme.pdf (using ps2pdf.exe)Emulated module Emulation target (using Emulator)

Emulated module

Emulator

Emulation target

Emulation scheme

A is intelligible if C is intelligible

or if E and B are intelligible

Equivalently:A is intelligible if

C or E are intelligible and

C or B are intelligible

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Changes in Dependency Graph

• A dependency graph is rarely static:– Modules become obsolete and disappear from system’s

and/or users’ profiles– New modules appear (e.g., new emulators created, new

versions of modules appear)– Errors, flaws or problems may be spotted in the original

modeling of the dependencies– Change of focus, perspective, needs or granularity of

modules and dependencies

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Handling Change

• Two types of change operations:– Atomic (trivial, one-step operations)– Complex (sequences of atomic operations)

• Requirement #1: Validity– Result makes sense (e.g., profiles contain known modules,

dependencies relate known modules etc)– Hard constraint: spawns side-effects or is blocked (rejected)

• Requirement #2: Self-intelligibility– System and user profiles should be self-intelligible– Soft constraint: spawns a notification

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Change Operations (Summary)

Change OperationApplies

on graphApplies on TS

Applies on Tu

Add Module

Delete Module

Add Dependency

Delete Dependency

Replace Module

Upgrade Backwards Compatible Module

Add Emulation Scheme

Atomic

Complex

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Conclusion and Future Work

• Provided a framework for modeling dependencies– Very general mechanism– Allows determining the modules required for a digital object

to be intelligible– Applications in digital preservation

• Our purpose:– To provide a framework (i.e., a tool) not a methodology (this

is application-dependent)

• Future work– Devise efficient algorithms for determining intelligibility– Determine computational complexity

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Thank you…

This work was partially supported by the EU project CASPAR (FP6-2005-IST-033572)