A Theory for Model-based Transformation Applied to Computer-Supported Preservation in Digital Archives Thomas Triebsees Universität der Bundeswehr München Department of Computer Science [email protected] Tucson, 27th March 2007 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 1 Agenda I. Research Context II. Motivating Example III. Declarative, Preservation-Centric Approach for Model Transformation IV. Preservation Language V. Results / Conclusions / Remarks Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 2 Research Context Long-term preservation of digital material Two facets: o Preservation procedure o Technical environment Preservation approaches: o Emulation o Migration o Hybrid } preserve information Technical environment o usually highly modularized and complex Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 3 Motivating Example Customer User Archive Archiver INGEST Browser extractMetadata storePerm CI EXPOSE Permanent Storage PStorage 1 PStorage 2 store respond BII UI Web Storage PStorage m Server 1 Server 2 ... REQUEST / RESPONSE Server n ... Transformation Integratable into system specifications Appropriate language elements Abstraction from different implementations Contribution: Declarative, domain-specific, preservation-centric language that facilitates to specify preservation requirements Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 4 III. Declarative, Preservation-Centric Approach for Model Transformation Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 5 Approach – System Model and Transformation Semantics Model elements -Typed Entities -Associations -Functions Transformation algorithm = sequence of basic operations Archive State A A System State Archive A' System State A' basic operation (create object) Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science System State A'' basic operation (set association) 6 Approach - Preservation Concept (= semantic property) implements Context 1 implements … specify preservation of … Context n defines Constraints Preservation language source context respect Transform. algorithms Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science used to generate / implement target context 7 Example – Abstraction through Contexts and Concepts Context Concept Context AWeb BWeb Website AWeb <name> src Website 0..1 φ (FOPL) eP * 0..1 1 Folder 1 1 … … <name>.html … <name> HTMLFile 1 BWeb <name>.html html * File … * Tag … resources trg PDFFile ψ (FOPL) Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science … … … … 8 Example – Specifying the Preservation Task Calculation Concept Website source <name> AWeb start.html … … <name>.html … Website calc.pdf 0..1 overview <name> eP 1 Folder doclist.html <name>.html 1 HTMLFile html … … calculation2005 … … EXPOSE δ … resources BWeb … … … Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science ? 9 Example - Typed Entities start.html HTMLFile start.html <html> <head/> h:HTML name : String location : String content : Tag <html> t11:Tag <body> … <a href=“…“></a> … </body> </html> <head> <body> t111:Tag t112:Tag <title> <a> t1111:Tag t1121:Tag Tag name : String attrs : Seq<String x String> content : Seq<(String | Tag> Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 10 IV. Preservation Language Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 11 Preservation Language – Transformation Constraints Archive State A' System A h → HTMLFile h Archive A' System State A' h‘ trans(δ | h → h‘) h:HTMLFile δ name = "start.html" location = "/… /source" content = <...> Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science δ(h):HTMLFile name = ? location = ? content = ? 12 Preservation Language – Object Preservation Constraints h → HTMLFile trans(δ | h → h‘) presO(h → HTMLFile, h[HTMLFile-{ location, }]) content post(δ) ≡ { name(h‘) = name(h) } HTMLFile-{ location, content } h:HTMLFile name name = "start.html" location = "/… /source" content = <...> δ(h):HTMLFile name = "start.html" location = ? content = <...> δ Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 13 Preservation Language – Concept Preservation Constraints presK({w → Website}, Website(w,f,h), AWeb, BWeb) location, presO(h → HTMLFile, h[HTMLFile-{ content }]) Concept Website Context AWeb w: „Calculation“ Context BWeb δ „Calculation“ δ(w): ____________ eP eP f: „source“ δ(f): ________ „source“ „start.html“ δ(h): __________ f‘: „html“ f‘‘: „resources“ h: „start.html“ Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 14 V. Results / Conclusion / Remarks Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 15 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 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 16 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 Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 17 Subject to your questions… Thomas Triebsees Universität der Bundeswehr München Department of Computer Science [email protected] Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 18 Constraint-based Migration Advantages of declarative approach easily integratable into system specifications focus on critical issues abstraction from implementation, thus platform independent formal treatment possible Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science 19 Approach Conceptual overview source model instance concept def. target model instance constraints (1) Preprocessing (2) Concept recognition (3) Algorithm generation (4) Algorithm execution object model extended object model migration alg. target object model Thomas Triebsees, Uwe M. Borghoff, Dptmt. of Computer Science (5) Postprocessing 20
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