1. NERC DataGrid Vocabulary Workshop, RAL, February 25, 2009 NERC DataGrid Vocabulary Server Description

2. NERC DataGrid Outline Vocabulary Server:  Data model  Implementation  Content  Usage  Development path

3. NERC DataGrid Vocabulary Server Data Model  The fundamental building block of the data model is a term, which is equivalent to a SKOS “concept”  Each term has:  Key: a semantically neutral string that forms the basis of a URN  Label: a human-readable name for the concept  Alternative label: used for abbreviations  Definition: more verbose explanation of the concept

4. NERC DataGrid Vocabulary Server Data Model  The terms are aggregated into lists equivalent to SKOS ‘collections’  Each list is given a semantically neutral identifier (4-byte string)  Lists may aggregated in ‘Superlists’  Each ‘Superlist’ is given a semantically opaque identifier (bytes 1-3 of the component list identifiers)

5. NERC DataGrid Vocabulary Server Data Model  The ‘Superlist’ concept was inherited from 1980s BODC infrastructure  It has no parallel in any knowledge representation standard  It is has the unpleasant side effect of giving terms alternative possible URNs  Its deprecation is becoming a priority

6. NERC DataGrid Vocabulary Server Implementation  Server back end is an Oracle relational database  All terms are stored in a single table  List and superlist aggregations implemented as a 2-level indexing table hierarchy  Heavily defended by constraints and triggers  Fully automated timestamps and update ‘fingerprints’  Fully automated audit trails  Fully automated list and superlist versioning

7. NERC DataGrid Vocabulary Server Implementation  Term URLs, list URLs and API calls invoke Java applications that submit SQL queries and wrap up the output as XML documents

8. NERC DataGrid Vocabulary Server Implementation  Why not XML?  Grew out of an integral part of the BODC Oracle infrastructure  Experiments with XML – particularly OWL – technology did not go well  Maintenance tools seem less effective  Navigation difficulties through very large XML documents  Performance issues with lists containing 20000+ terms  XML has benefits such as access to inference engines, so worth persevering  Answer might be to have operational XML builds from a relational back end

9. NERC DataGrid Vocabulary Server Content  Server Contents (2009-02-10)  76 public superlists  125 public lists  124701 public terms  80987 public mappings (RDF triples)  Some of the subject areas covered  Parameters  Platforms  Instruments  Coverage terms  Geographic keywords

10. NERC DataGrid Vocabulary Server Usage  Server Usage for 2008 (2009 to 2009-02-10 in brackets)  4793116 (607172) total hits  56232 (7134) vocabulary catalogue downloads  78708 (10233) vocabulary term/list downloads  1367 (433) vocabulary map downloads  2479 (73) term searches  1501 (74) term verifications  Rest of total is robots mining semantic links (getRelatedRecordByTerm method)

11. NERC DataGrid VS Development Path  Version 1.1 current operational version  Version 1.2 currently under development  Transparent upgrade (no change to WSDL)  Bug fix and activation of versioned list serving  Additional service API providing list content upgrade functionality to authenticated, authorised external users

12. NERC DataGrid VS Development Path  Version 2.0 currently being designed  Revisit back end design  Governance labelling  Deprecation support  Introduce more XML technology?  Introduce formally-registered, truly permanent URNs  Single RESTful API giving both read and write access through appropriate HTTP methods  Output document revision to SKOS 2008

13. NERC DataGrid VS Development Path  Whatever happens with V2.0 we will not annoy a large and very active user base through change  Both versions will therefore run in parallel until V1.2 calls are no longer logged