Mind the (Intelligibility) Gap

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

2. 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 • … Giorgos Flouris, ECDL-07

3. 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) Giorgos Flouris, ECDL-07

4. 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 Giorgos Flouris, ECDL-07

5. Modeling Example readme.txt Wordpad software ORNotepad software Notepad software Wordpad software Greek language Windows software Monitor computer system power outlet Giorgos Flouris, ECDL-07

6. Dependency Graphs {A} 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} {E} {B,C} {G} {D} {C} {F} {B} Giorgos Flouris, ECDL-07

7. Preservation System A A D A A E C F F Preservation Setting DependencyGraph D System Profile: TS User Profile: Tu All interesting modules are modeled here Giorgos Flouris, ECDL-07

8. Intelligibility Issues {A} 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) {E} {B,C} {G} {D} {C} {F} {B} Giorgos Flouris, ECDL-07

9. Emulators (Migrators, Translators, …) 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) Unintelligible Emulated module Emulation target A is intelligible if C is intelligible orif E and B are intelligible Equivalently:A is intelligible if C or E are intelligible andC or B are intelligible {A} B A {C,E} {C} {C,B} E Not in profile Emulation scheme Emulator Giorgos Flouris, ECDL-07

10. 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 Giorgos Flouris, ECDL-07

11. 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 Giorgos Flouris, ECDL-07

12. Change Operations (Summary) Atomic Complex Giorgos Flouris, ECDL-07

13. 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 Giorgos Flouris, ECDL-07

14. Thank you… This work was partially supported by the EU projectCASPAR (FP6-2005-IST-033572) Giorgos Flouris, ECDL-07