steps towards a theory of information preservation giorgos flouris, carlo meghini istituto di...

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)

23/03/2007 Giorgos Flouris, 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


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)


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


Preservation Types

The first letter of the

English alphabet

The first letter of the

English alphabet

PRODUCER CONSUMER

Kno

wle

dge

Leve

lS

ymbo

l Le

vel

Understands Concept

Reads SymbolWrites Symbol

Understands Concept

Reads BitsWrites Bits

KR Level

Information Preservation

Data (or Object) Preservation

Bit Preservation

A

01000001

A

01000001

Time


Preservation TypesExample

City Temperature Date

Athens 12 08/03/07

Pisa 11 06/03/07

Edinburgh 8 11/03/07

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)


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


StaticsSchematically


Information to be Preserved:Questions and Answers

• Digital object: a set of questions and answers– Not all information in 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– …


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, ⊧>

IPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧


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)


Purpose of Preservation


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


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– …


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


DynamicsSchematically (Idealized Case)

Producer Consumer


DynamicsSchematically (General Case)

Producer Consumer

Expanded

Various levels of preservation:complete, essential, modulo logical equivalence, indirect, approximate, partial, …


DynamicsIPS Evolution Structure (IPSES)

IPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

ProducerIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

ExpandedIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

Consumer

⊇

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)

IPSES


Putting it All TogetherGeneral Ideas

11/03/078Edinburgh

06/03/0711Pisa

08/03/0712Athens

DateTemperatureCity

11/03/078Edinburgh

06/03/0711Pisa

08/03/0712Athens

DateTemperatureCity

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 Preservation Bits are not corrupt

Data PreservationBits’ format is understood/read

Information PreservationInformation is understood

The first letter of the English

Alphabet


alphabet

PRODUCER CONSUMER

Kno

wle

dge

Leve

lS

ymb

ol

Leve

l

Understands Concept


Understands Concept


KR Level



Bit Preservation

A

01000001

A

01000001

Time


Alphabet


alphabet

PRODUCERPRODUCER CONSUMERCONSUMER

Kno

wle

dge

Leve

lS

ymb

ol

Leve

l

Understands Concept


Understands Concept


KR Level



Bit Preservation

A

01000001

A

01000001

Time


Putting it All TogetherStatics

IPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

IPS

UCK Digital ObjectUCK Digital Object

L T Q ansL TL T Q ansQ ans

LL V VI P PC ⊧LL V VI P PC ⊧

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


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


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)

Producer Consumer

Expanded

IPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

ProducerIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

ExpandedIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

Consumer

⊇IPSES

IPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

ProducerIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

IPS




ProducerIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

ExpandedIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

IPS




ExpandedIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

ConsumerIPS

UCK Digital Object

L T Q ans

LL V VI P PC ⊧

IPS




Consumer

⊇IPSES


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


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).


BACKUP SLIDES


The last letter of the

English alphabet

Preservation TypesRevisited

The 6th letter of the Greek

Alphabet

PRODUCER CONSUMER

Kno

wle

dge

Leve

lS

ymbo

l Le

vel

Understands Concept


Understands Concept


KR Level



Bit Preservation

Z

01011010

Z

01011010


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


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


Contents of a UCK

Common Knowledge

Knowledge P1

Knowledge P2

Knowledge P3

Digital Object

Knowledge C1

Knowledge C2

UCK

Producer Intended Consumer


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

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