Steps Towards a Theory of Information Preservation

1. Steps Towards a Theory of Information Preservation Giorgos Flouris, Carlo Meghini Istituto di Scienza e Tecnologie dell’ Informazione (ISTI) CNR, Pisa, Italy {flouris,meghini}@isti.cnr.it Invited Talk (PresDB-07)

2. Introduction • Preservation: • Very important, difficult and interesting problem • Need for preservation is self-evident • Notes on this work: • Ongoing work for CASPAR (suggestions welcome) • About digital objects (not about databases, but can be applied to databases) • The focus of this work is not to perform preservation, but to describe formally what it means to perform preservation Giorgos Flouris, PresDB-07

3. Purpose We are trying to come up with a formal, mathematical, logic-based description of preservation as a scientific discipline, to the end of deriving a methodology resting on solid grounds (then, we will try to apply this methodology to CASPAR) Giorgos Flouris, PresDB-07

4. The Need for a Theory of Information Preservation • Why is such a theory important? • A formal, theoretical, mathematical framework allows the proof of impossibility and existential results • Allows us to ground existing (and future) methods upon a common formalism for comparison • Provides a set of formal desirable properties for existing and future preservation methods • Allows proving that a preservation method works well (or does not work well) • Where practitioners believe, a theory can prove Giorgos Flouris, PresDB-07

5. PRODUCER CONSUMER Preservation Types KR Level The first letter of the English alphabet The first letter of the English alphabet Knowledge Level Understands Concept Understands Concept Information Preservation A A Writes Symbol Reads Symbol Data (or Object) Preservation Symbol Level 01000001 01000001 Writes Bits Reads Bits Bit Preservation Time Giorgos Flouris, PresDB-07

6. Preservation TypesExample Bit Preservation: Database is not corrupt (error correction techniques, backups, refreshment of media) Data Preservation: Database can be opened (preserve format specification) Information Preservation: Database can be understood (temperatures in Celsius, dates in dd/mm/yy) Giorgos Flouris, PresDB-07

7. StaticsDigital Object and UCK • A digital object depends on external information: • Bit Format (ASCII codes, integer representation, …) • Symbols’ Format (23/03/07 or 03/23/07) • Background Knowledge (what is the meaning of 23/03/07) • A digital object is attached to a single Underlying Community Knowledge (UCK) that contains this information • Therefore: • A digital object carries no meaning by itself • Its meaning (semantics) is derived from the attached UCK Giorgos Flouris, PresDB-07

8. StaticsSchematically Giorgos Flouris, PresDB-07

9. Information to be Preserved:Questions and Answers • Digital object: a set of questions and answers • Not all informationin a digital object needs to be preserved • Example: a document (content, format, fonts, pagination) • The exact information to be preserved depends on: • Type of digital object • Producer’s intentions • Digital object’s intended reader (Designated Community) • Legal issues • Practical considerations • … Giorgos Flouris, PresDB-07

10. IPS Digital Object UCK L T Q ans LL V PC ⊧ VI P StaticsInformation Preservation Structure (IPS) • IPS = UCK + Digital Object • UCK: <L,T> • Digital Object: <Q,ans> • L is further broken down: • L= <LL, V, VI, P, PC, ⊧> Giorgos Flouris, PresDB-07

11. IPS and Preservation Models • Preservation models provide a methodological framework for determining the content of an IPS • OAIS (ISO standard 14721:2003) • Representation Information (UCK) • Structural Information • Semantic Information • Preservation Description Information (questions and answers) • Provenance • Reference • Context • Fixity • Digital object’s content (questions and answers) Giorgos Flouris, PresDB-07

12. Purpose of Preservation Giorgos Flouris, PresDB-07

13. Preservation and Change • UCK evolves • If digital objects remained the same, they would be either unreadable or would carry the wrong meaning • Thus we need a methodology that will indicate the appropriate changes to all digital objects attached to a UCK, as a function of: • The old digital object • The old UCK (producer’s UCK) • The new UCK (consumer’s UCK) • The UCK evolution specification Giorgos Flouris, PresDB-07

14. Belief Change, Ontology Evolution and Information Preservation (1) • Initial thought: use well-established methods from belief change (belief revision) and ontology evolution • Not possible, in general: • The UCK may be a logic not supported by the above fields • Changes may affect the logic itself • Changes may be of infinite nature • Input/output may be different • Example: Roman to Arabic numerals • III 3 • IV 4 • … Giorgos Flouris, PresDB-07

15. Belief Change, Ontology Evolution and Information Preservation (2) • However, it is possible under some assumptions: • The logic does not change • The logic in UCK is supported • Old UCK and digital object are known, evolution is known • Change can be finitely described using standard models • Example from astronomy: • Pluto was a Planet • Planet definition changed recently (24/08/06, Prague) • Pluto reclassified as a Dwarf Planet Giorgos Flouris, PresDB-07

16. DynamicsSchematically (Idealized Case) Producer Consumer Giorgos Flouris, PresDB-07

17. DynamicsSchematically (General Case) Producer Consumer Expanded Various levels of preservation:complete, essential, modulo logical equivalence, indirect, approximate, partial, … Giorgos Flouris, PresDB-07

18. Producer Expanded Consumer IPS IPS IPS Digital Object Digital Object Digital Object UCK UCK UCK L L L T T T Q Q Q ans ans ans LL LL LL V V V PC PC PC ⊧ ⊧ ⊧ VI VI VI P P P DynamicsIPS Evolution Structure (IPSES) ⊇ IPSES Mapping needs a finite representation: Turing Machines IPSES’ definition is incomplete Need a way to compute the green arrow from the information given (old digital object, producer’s UCK, consumer’s UCK, IPSES) Giorgos Flouris, PresDB-07

19. Putting it All TogetherGeneral Ideas What is preservation? Preservation is the process of retaining the meaning of a digital object unaltered for readers with different background, software, hardware etc What are the preservation types? Bit PreservationBits are not corrupt Data PreservationBits’ format is understood/read Information PreservationInformation is understood Giorgos Flouris, PresDB-07

20. Putting it All TogetherStatics What is a digital object? A digital object is a sequence of bits (no meaning) What gives meaning to a digital object? The underlying (often implicit) format, knowledge, symbols’ meaning etc, represented by UCK What should be preserved? A set of questions and their answers How do we determine the content of an IPS? Preservation models can help Giorgos Flouris, PresDB-07

21. Putting it All TogetherDynamics (General) Why is preservation needed? Underlying knowledge (UCK) evolves; if digital objects remained the same, they would be not understood or be misunderstood When is preservation achieved? When digital objects retain their meaning Can other research fields help? Belief Revision and Ontology Evolution, but only partially Giorgos Flouris, PresDB-07

22. Putting it All TogetherDynamics (IPSES) How can we describe UCK evolution? Using an expanded UCK, plus a mapping and a number of correspondences between the UCKs Is preservation always possible? No; various levels of preservation How should digital objects evolve? Open question; a function of the old digital object, the two UCKs and the UCK evolution information (IPSES) Giorgos Flouris, PresDB-07

23. Future Work • Calculate the evolution of the digital object as a function of: • Old digital object • Producer’s UCK • Consumer’s UCK • IPSES (evolution information) • Ongoing work: refinements might be required • Extensive testing of the theory (real-world examples) • Tie the theory to more useful in practice structures Giorgos Flouris, PresDB-07

24. The End Acknowledgements This work was carried out during Giorgos Flouris’ tenure of an ERCIM “Alain Bensoussan” Fellowship Programme. This work was partially supported by the EU project CASPAR (FP6-2005-IST-033572). Giorgos Flouris, PresDB-07

25. BACKUP SLIDES Giorgos Flouris, PresDB-07

26. PRODUCER CONSUMER The last letter of the English alphabet Preservation TypesRevisited KR Level The 6th letter of the Greek Alphabet Knowledge Level Understands Concept Understands Concept Information Preservation Z Z Writes Symbol Reads Symbol Symbol Level Data (or Object) Preservation 01011010 01011010 Writes Bits Reads Bits Bit Preservation Giorgos Flouris, PresDB-07

27. Preservation TypesJoke Analogy • In order to laugh at a joke, you must: • Hear the joke (bit preservation) The sound waves should reach your ears; if you are in another room, you won’t laugh at the joke • Understand the joke (data preservation)You should understand the language; if I say a joke in Greek, you won’t laugh at the joke • Understand the context of the joke (information preservation)You should understand what the joke is about; if I say a joke about the political situation in Greece, you won’t laugh at the joke Giorgos Flouris, PresDB-07

28. StaticsUnderlying Community Knowledge (UCK) • UCK: a logical formalism, plus a logical theory • Because logics are: • Formal • Able to express knowledge • Suitable to capture question-answering (using inference) • Well-studied, mature, well-established field with rich results • Allow building theories to express background knowledge • We don’t embrace any particular logic Giorgos Flouris, PresDB-07

29. UCK Contents of a UCK Producer Intended Consumer Digital Object Knowledge P3 Knowledge P2 Knowledge C2 Knowledge P1 Knowledge C1 Common Knowledge Giorgos Flouris, PresDB-07

30. DynamicsNotes on IPSES • IPS Evolution Structure (IPSES): • IPSES = UCK + mapping • Exact specification of the change (no side-effects) • Usually change is partially specified (has side-effects) • Determining side-effects is orthogonal to preservation • Change may be infinite (finite representation needed) • Example: Roman and Arabic numerals • Need Turing Machines to represent the mapping Giorgos Flouris, PresDB-07