Thomas Triebsees Universität der Bundeswehr München Department of Computer Science

Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 1

Thomas TriebseesUniversität der Bundeswehr München

Department of Computer Science

[email protected]

Tucson, 27th March 2007

A Theory for Model-based TransformationApplied to Computer-SupportedPreservation in Digital Archives


Agenda

I. Research Context

II. Motivating Example

III. Declarative, Preservation-Centric Approach for Model Transformation

IV. Preservation Language

V. Results / Conclusions / Remarks


Research Context

Long-term preservation of digital material

Two facets:

o Preservation procedure

o Technical environment

Preservation approaches:

o Emulation

o Migration

o Hybrid

Technical environment

o usually highly modularized and complex

} preserve information


Motivating Example

PStorage 1 PStorage 2 PStorage m

...Server 1

...

Archiver Browser

Server 2 Server n

UICIINGEST REQUEST /RESPONSE

EXPOSE BII

ArchiveCustomer User

Permanent Storage Web Storage

storePerm

extractMetadata store

respond

TransformationTransformation

Contribution: Declarative, domain-specific, preservation-centric language that facilitates to specify preservation requirements

Integratable into system specifications

Appropriate language elements

Abstraction from differentimplementations


III. Declarative, Preservation-Centric Approach for Model Transformation


Approach – System Model and Transformation Semantics

-Typed Entities

-Associations

-Functions

Model elements

Archive State AArchive State ASystem State A Archive State A'Archive State A'System State A'

basic operation(create object)

System State A''

basic operation(set association)

Transformation algorithm = sequence of basic operationsTransformation algorithm = sequence of basic operations


Approach - Preservation

Preservation Preservation languagelanguage

ConstraintsConstraints

Transform.Transform.algorithmsalgorithms

defines

used togenerate /implement

respect

Concept (= semantic property)Concept (= semantic property)

Context 1Context 1 Context nContext n…

source context target context

implements implements

…specify pre-servation of


Example – Abstraction through Contexts and Concepts

Website

HTMLFileFolder

File

PDFFile

Tag

eP

0..1

11

1

*

1

*

*

0..1

<name>

<name>.html

<name>

html

resources

<name>.html

Concept Website

……

…

……

…

……

…

src

trg

Context AWebContext BWeb

φ (FOPL)

ψ (FOPL)

AWeb

BWeb


Example – Specifying the Preservation Task

source

calculation2005

overview

calc.pdf

doclist.html

start.html

Website

eP

0..1

<name>

<name>.html

<name>

html

resources

<name>.html

……

…

……

…

……

…

AWeb

??

HTMLFileFolder

11

… …

δ

Concept Website

BWeb

Calculation

EXPOSE


Example - Typed Entities

name : Stringattrs : Seq<String x String>content : Seq<(String | Tag>

name : Stringattrs : Seq<String x String>content : Seq<(String | Tag>

Tag

<html><head/>

<body> … <a href=“…“></a> …</body></html>

<html><head/>

<body> … <a href=“…“></a> …</body></html>

start.html name : Stringlocation : Stringcontent : Tag

name : Stringlocation : Stringcontent : Tag

HTMLFile start.htmlstart.html

h:HTMLh:HTML

<html><html>

t11:Tagt11:Tag

<head><head>

t111:Tagt111:Tag<body><body>

t112:Tagt112:Tag

<title><title>

t1111:Tagt1111:Tag

<a><a>

t1121:Tagt1121:Tag


IV. Preservation Language


Preservation Language – Transformation Constraints

h → HTMLFile

name = "start.html"location = "/… /source"content = <...>


h:HTMLFile

name = ?location = ?content = ?

name = ?location = ?content = ?

δ(h):HTMLFileδ

trans(δ | h → h‘)trans(δ | h → h‘)

Archive State A'Archive State A'System State A Archive State A'Archive State A'System State A'

h h‘


HTMLFile-{ }

name

location,content



h:HTMLFile

Preservation Language – Object Preservation Constraints

name = "start.html"location = ?content = <...>

name = "start.html"location = ?content = <...>

δ(h):HTMLFile

δ

name

trans(δ | h → h‘)trans(δ | h → h‘)

h → HTMLFile

post(δ) ≡ { name(h‘) = name(h) }

presO(h → HTMLFile, h[HTMLFile-{ }])location,content


Preservation Language – Concept Preservation

Constraints

w: „Calculation“

f: „source“

Context AWeb

δ

presK({w → Website}, Website(w,f,h), AWeb, BWeb)

Concept Website

h: „start.html“

eP

δ(w): ____________

δ(f): ________ δ(h): __________

eP

Context BWeb

f‘: „html“ f‘‘: „resources“

presO(h → HTMLFile, h[HTMLFile-{ }])location, content

„start.html“„source“

„Calculation“


V. Results / Conclusion / Remarks


Conclusion

Constraint definitions show generality (abstraction

from specification language)

Prototypical implementation available

Website migration example:o ≈ 300 files

o ≈ 20 concepts

o ≈ 700 constraints

o ≈ 2300 affected objects


Conclusion

Strengths: State-based approach

Powerful object model

Abstraction via concepts; specification language need not necessarily

be FOPL

Intuitive constraint definition for application domain

Coherently formal underpinning

Limits: Generation of parallel migration algorithms

Undecidability of FOPL

Generating algorithms for comprehensive model reconstructions

Efficiency


Subject to your questions…

Thomas TriebseesUniversität der Bundeswehr München

Department of Computer Science

[email protected]


Constraint-based Migration

easily integratable into system specifications

focus on critical issues

abstraction from implementation, thus platform independent

formal treatment possible

Advantages of declarative approach


Approach

Conceptual overview

(1) Pre-processing

object model

source modelinstance

(4) Algorithm execution

target objectmodel

(2) Concept recognition

concept def.

extendedobject model

(3) Algorithm generation

constraints

migration alg.

(5) Post-processing

target modelinstance

Thomas Triebsees Universität der Bundeswehr München Department of Computer Science

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