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National Geospatial Digital Archive

National Geospatial Digital Archive. Greg Janée University of California at Santa Barbara. A misadventure in preservation. 1976 Viking probes go to Mars soil data is analyzed for evidence of life 1999 USC neurobiologist Joseph Miller asks for data NASA has data on tape! But...

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National Geospatial Digital Archive

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  1. National Geospatial Digital Archive Greg Janée University of California at Santa Barbara

  2. A misadventure in preservation • 1976 • Viking probes go to Mars • soil data is analyzed for evidence of life • 1999 • USC neurobiologist Joseph Miller asks for data • NASA has data on tape! • But... • tapes coded “in a format so old that the programmers who knew it had died” Greg Janée • DCC seminar • 2005-09-27

  3. Paradox of preservation • Is the data valuable? • yes: had to travel to another planet to get it • Is the data being used? • no • perhaps never again • How much am I willing to pay for its preservation? • as close to zero as possible Greg Janée • DCC seminar • 2005-09-27

  4. Is it worth preserving? • Keith’s equation*: • (current value) = (intrinsic value) - (cost to use) • Greg’s equation: • item is worth preserving for time duration T if: • (intrinsic value) * ProbT(usage) >T(preservation costs) + (cost to use) *apologies to Keith Johnson, Stanford libraries Greg Janée • DCC seminar • 2005-09-27

  5. Project genesis • NDIIPP • Library of Congress, 2000 • $100M • http://www.digitalpreservation.gov/ • NGDA • UCSB (MIL) & Stanford (Branner Library) • $2.6M, 3 years • geospatial data • http://www.ngda.org/ Greg Janée • DCC seminar • 2005-09-27

  6. Greg Janée • DCC seminar • 2005-09-27

  7. Project goal • “How can we preserve geospatial data on a national scale and make it available to future generations?” • No focus on a particular collection • Geospatial data • discrete chunks • relatively highly-structured, well-defined • but 90% of our work is generic Greg Janée • DCC seminar • 2005-09-27

  8. Idea #1 • Archival has to be cheap & easy • must be distributed • little incentive, no funding • not sexy Greg Janée • DCC seminar • 2005-09-27

  9. NGDA approach • Compromise: define cheap archive • fundamental approach: preservation by co-archival of object semantics • ingest: one step up from crawling • web access • notable for what’s missing: discovery, usability • Foundation for additional functionality • e.g., migration • prototype archives will offer ADL, OAI access Greg Janée • DCC seminar • 2005-09-27

  10. Idea #2 • Archival systems must be designed with their own demise in mind • archival objects will long outlive any system that manages them • system-level migrations will occur • at inopportune times Greg Janée • DCC seminar • 2005-09-27

  11. system handle resolver handle resolver storage database database database database fragile Typical repository architecture Greg Janée • DCC seminar • 2005-09-27

  12. access ingest Web ADL OAI bulk loader archival system storage subsystem standard, public data model databases, caches, etc. NGDA architecture Greg Janée • DCC seminar • 2005-09-27

  13. Post-NGDA architecture Web storage subsystem standard, public data model Greg Janée • DCC seminar • 2005-09-27

  14. Storage system requirements • Req’s: • associate UUIDs/RIDs with bitstreams • retrieve global/local bitstream by UUID/RID • determine (parent) UUID of any bitstream • list all UUIDs • Satisfied by: • any filesystem • any kind of UUIDs • tag:library.ucsb.edu,2005:identifier Greg Janée • DCC seminar • 2005-09-27

  15. manifest UUID RID component Archival objects UUID Greg Janée • DCC seminar • 2005-09-27

  16. Archival object representation • Components are files • Manifest is an XML document • Other approaches • OAIS: archival information packages (AIPs) • XMLtape Greg Janée • DCC seminar • 2005-09-27

  17. Ingest • Ingest template defines • common structure of objects to be ingested • necessary validations • associations to other objects • assumes pre-loading of semantic definitions • policies, rights, etc. • Represents choke point • requires human evaluation Greg Janée • DCC seminar • 2005-09-27

  18. Format registry • We’re developing one • who isn’t? • Serves as archive of format specifications • How broadly to interpret “format”? • traditional file format • product • series, collection, arbitrary set Greg Janée • DCC seminar • 2005-09-27

  19. “dessicated” version Format dependencies • Consider dependency graph induced by format specifications • Def: a format is recoverable if the format of its specification is recoverable • Axioms: plain text, HTML are recoverable GIF PDF GeoTIFF CSS TIFF plain text HTML Greg Janée • DCC seminar • 2005-09-27

  20. Challenges • Making ingest easy, easier, easier-er, ... • GIS formats • very complex: topology, layer, coverage, project • proprietary • MODIS • multiple petabytes • format (HDF) is not well-defined • moving to on-demand computation of products • lineage important • copious additional semantics Greg Janée • DCC seminar • 2005-09-27

  21. Misadventure, redux • What if there had been an NGDA-like solution? • format specification would have been archived • Limitations • data not necessarily immediately usable • format specification itself not necessarily viewable • But limitations can be addressed according to usage, available resources Greg Janée • DCC seminar • 2005-09-27

  22. Questions for you • Archival systems • definition? functionality? • Storage systems • definition? functionality? • Archival object representation • discrete files vs. AIPs? • GIS formats • “dessicated” form? Greg Janée • DCC seminar • 2005-09-27

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