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

2. 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. 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. 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. 5 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science III.Declarative, Preservation-Centric Approach for Model Transformation

6. 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. 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. 8 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Example – Abstraction through Contexts and Concepts Website HTMLFile Folder File PDFFile Tag eP 0..1 1 1 1 * 1 * *.html html resources.html Concept Website … … … … … … … … … src trg Context AWebContext BWeb φ (FOPL) ψ (FOPL) AWeb BWeb

9. 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. 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. 11 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science IV.Preservation Language

12. 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. 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. 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. 15 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science V.Results / Conclusion / Remarks

16. 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. 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. 18 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science Subject to your questions… Thomas Triebsees Universität der Bundeswehr München Department of Computer Science Thomas.Triebsees@unibw.de

19. 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. 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