1 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Thomas Triebsees Universität der Bundeswehr München Department of Computer Science Tucson, 27th March 2007 A Theory for Model-based Transformation Applied to Computer-Supported Preservation in Digital Archives

2 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Agenda I.Research Context II.Motivating Example III.Declarative, Preservation-Centric Approach for Model Transformation IV.Preservation Language V.Results / Conclusions / Remarks

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

4 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Motivating Example PStorage 1PStorage 2 PStorage m... Server 1... ArchiverBrowser Server 2Server n UICI INGEST REQUEST / RESPONSE EXPOSE BII Archive Customer User Permanent StorageWeb Storage storePerm extractMetadata store respond Transformation Contribution: Declarative, domain-specific, preservation-centric language that facilitates to specify preservation requirements Integratable into system specifications Appropriate language elements Abstraction from different implementations

5 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science III.Declarative, Preservation-Centric Approach for Model Transformation

6 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Approach – System Model and Transformation Semantics -Typed Entities -Associations -Functions Model elements Archive State A System State A Archive State A' System State A' basic operation (create object) System State A'' basic operation (set association) Transformation algorithm = sequence of basic operations

7 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Approach - Preservation Preservationlanguage Constraints Transform.algorithms defines used to generate / implement respect Concept (= semantic property) Context 1 Context n … source context target context implements … specify pre- servation of

8 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Example – Abstraction through Contexts and Concepts Website HTMLFile Folder File PDFFile Tag eP * 1 * *.html html resources.html Concept Website … … … … … … … … … src trg Context AWebContext BWeb φ (FOPL) ψ (FOPL) AWeb BWeb

9 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Example – Specifying the Preservation Task source calculation2005 overview calc.pdf doclist.html start.html Website eP 0..1.html html resources.html … … … … … … … … … AWeb ? ? HTMLFile Folder 11 …… δ Concept Website BWeb Calculation EXPOSE

10 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Example - Typed Entities name : String attrs : Seq content : Seq name : String attrs : Seq content : Seq Tag … … … … start.html name : String location : String content : Tag name : String location : String content : Tag HTMLFile start.html h:HTML t11:Tag t111:Tag t112:Tag t1111:Tag t1121:Tag

11 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science IV.Preservation Language

12 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Preservation Language – Transformation Constraints h → HTMLFile name = " start.html" location = " /… /source" content = name = " start.html" location = " /… /source" content = h:HTMLFile name = ? location = ? content = ? name = ? location = ? content = ? δ(h):HTMLFile δ trans(δ | h → h‘) Archive State A' System State A Archive State A' System State A' h h‘

13 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science HTMLFile-{ } name location, content name = " start.html" location = " /… /source" content = name = " start.html" location = " /… /source" 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‘) h → HTMLFile post(δ) ≡ { name(h‘) = name(h) } pres O (h → HTMLFile, h[HTMLFile-{ }]) location, content

14 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Preservation Language – Concept Preservation Constraints w: „Calculation“ f: „source“ Context AWeb δ pres K ({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“ pres O (h → HTMLFile, h[HTMLFile-{ }]) location, content „start.html“ „source“ „Calculation“

15 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science V.Results / Conclusion / Remarks

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

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

18 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Subject to your questions… Thomas Triebsees Universität der Bundeswehr München Department of Computer Science

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

20 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Approach Conceptual overview (1) Pre- processing object model source model instance (4) Algorithm execution target object model (2) Concept recognition concept def. extended object model (3) Algorithm generation constraints migration alg. (5) Post- processing target model instance