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NERC DataGridNERC DataGrid
Vocabulary Workshop, RAL, February 25, 2009Vocabulary Workshop, RAL, February 25, 2009
NERC DataGridNERC DataGridVocabulary Server Vocabulary Server DescriptionDescription
NERC DataGridNERC DataGrid
OutlineOutline
Vocabulary Server:
Data model Implementation Content Usage Development path
NERC DataGridNERC DataGrid
Vocabulary Server Data ModelVocabulary 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
NERC DataGridNERC DataGrid
Vocabulary Server Data ModelVocabulary 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)
NERC DataGridNERC DataGrid
Vocabulary Server Data ModelVocabulary 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
NERC DataGridNERC DataGrid
Vocabulary Server ImplementationVocabulary 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
NERC DataGridNERC DataGrid
Vocabulary Server ImplementationVocabulary Server Implementation
Term URLs, list URLs and API calls invoke Java applications that submit SQL queries and wrap up the output as XML documents
NERC DataGridNERC DataGrid
Vocabulary Server ImplementationVocabulary 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
NERC DataGridNERC DataGrid
Vocabulary Server ContentVocabulary 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
NERC DataGridNERC DataGrid
Vocabulary Server UsageVocabulary 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)
NERC DataGridNERC DataGrid
VS Development PathVS 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
NERC DataGridNERC DataGrid
VS Development PathVS 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
NERC DataGridNERC DataGrid
VS Development PathVS 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