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Avoiding a Semantic Web Roadblock: URI Management and Ontology Evolution

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We highlight the importance of creating a set of guidelines for managing URIs during ontology evolution and linking open data. We examine some potential and actual negative impacts of making the wrong …

We highlight the importance of creating a set of guidelines for managing URIs during ontology evolution and linking open data. We examine some potential and actual negative impacts of making the wrong decision. For example, the new version of SKOS changes the semantics for existing terms without changing the URI. This adds a heavy load on developers of ontology-driven applications to keep them from breaking. Alternatively, minting a whole set of new URIs when the meaning for most of the terms is unchanged, causes an unnecessary proliferation of URIs that adds computational and conceptual overheads. We suggest a way forward based on examining two root causes of the problem: 1) URIs are overloaded and 2) there is no good technology for change management. As linked data grows and as applications are driven more and more by ontologies, the negative impacts of inadequate URI management could severely retard the growth of the semantic web.

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    • 1. Copyright © 2010 Michael Uschold. All rights reserved.
      Avoiding a Semantic Web Road Block: URI Management and Ontology Evolution
      Michael Uschold, PhD: Independent Consultant
      .
      Friday 25 June 2010
      Semantic Technology Conference , San Francisco, CA
      1
    • 2. Page 2
      Copyright © 2010 Michael Uschold. All rights reserved.
      Outline
      Examples of linked data in the wild
      Problems
      Root Causes
      What to do?
    • 3. Ontologies and Linked Data in the Wild: SKOS
      Simple Knowledge Organizing System (SKOS)
      Small vocabulary (20 terms)
      Evolve to new version
      Changes:
      Majority of terms are the same
      Change semantics of broader: no longer transitive
      3
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 4. Ontologies and Linked Data in the Wild: WordNet
      WordNet: lexical database for English language
      Large vocabulary
      Evolve to new version
      Changes:
      Majority of terms are the same
      Significant number of updates and changes
      4
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 5. Ontologies and Linked Data in the Wild: Open Biomedical Ontologies
      Open Biomedical Ontologies
      Very large vocabulary
      Interconnected ontologies
      Undergoing continual evolution (daily)
      Changes:
      Majority of terms are the same
      Significant number of updates and changes
      5
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 6. Versioning and URIs: Options
      Mint all new URIs, even for unchanged terms.
      Keep URIs the same, even when semantics changes.
      Mint new URIs only for changed terms.(including the ontology URI)
      Throw away old terms?
      Deprecate old terms for backwards compatibility?
      6
      Copyright © 2010 Michael Uschold. All rights reserved.
      When/whether to mint new URIs for terms in new versions?
    • 7. (A) Mint all new URIs: Impacts
      Usage Scenario
      Application loads ontology O1 and data D1
      New version: O2
      All new URIs,
      No idea which terms have different semantics
      New dataset D2, created and loaded into application
      Query using old URIsWRONG ANSWERS: Ignores data from new URIs
      7
      Copyright © 2010 Michael Uschold. All rights reserved.
      Maintenance headaches: find semantic matches
      Performance problems: if use owl:sameAs
      Broken applications
      Convenient for first time users.
    • 8. (B) Same URIs, Different Semantics: Impacts
      Usage Scenario
      Application loads ontology O1 and data D1
      Create application functionality that depends on O1
      New version: O2
      Some terms now have different semantics, but the same URIs,
      No idea which terms have different semantics
      New dataset D2, created and loaded into application
      Run functionality that depends on O1 semanticsWRONG ANSWERS: mixing different semantics
      8
      Copyright © 2010 Michael Uschold. All rights reserved.
      Maintenance Headaches: find semantic matches
      Broken Applications
      Convenient for first time users.
    • 9. (C) New URIs only for changed terms: Impacts
      Usage Scenarios
      No broken applications
      No performance problems
      No maintenance headaches
      Inconvenience of having same ontology with multiple namespaces.
      9
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 10. Pros and Cons
      10
      Copyright © 2010 Michael Uschold. All rights reserved.
      What would YOU do? WordNet, SKOS, Biomedical Ontologies
      What did THEY do?
    • 11. What Actually Happened?
      Open Biomedical Ontologies: (C)
      New URIs only for new terms, deprecate old terms
      SKOS: (B) Same URIs, Different Semantics
      WordNet: (A) Mint all new URIs, multiple times!
      http://wordnet.princeton.edu/~agraves/wordnet/0.9/
      http://xmlns.com/wordnet/1.6/
      http://www.w3.org/2006/03/wn/wn20/instances/
      http://www.loa-cnr.it/wn30/instances/
      11
      Copyright © 2010 Michael Uschold. All rights reserved.
      But wait, there’s more:
      http://purl.org/vocabularies/princeton/wn30/
      http://www.ontologyportal.org/WordNet.owl#WN30-200662589
    • 12. Why no Uproar?
      SKOS is not a standard
      SKOS is not used by that many people
      It’s just life, people get by
      Few ontology-driven applications
      BUT: this is changing, and business as usual could result in a Semantic Web Roadblock down the road.
      12
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 13. Another Example: DBpedia and Yago
      DBpedia published, without any ontology
      YAGO team created ontology from DBpedia
      Subset of Wikipedia category hierarchy
      Only when aligned with WordNet hierarchy
      http://www.mpii.de/yago/resource/wordnet_calculator_102938886
      DBpedia team added Yago Classes to their datasets, but different URIs were used.
      http://dbpedia.org/class/yago/Calculator102938886
      ISSUES:
      Proliferation of URIs, OWL:sameAs, Performance
      A lot of semantics hidden in names.
      13
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 14. Problems and Root Causes
      14
      Ontology-driven applications break
      Maintenance
      Issues
      Performance Issues
      URIs Overloaded
      (especially w/ UIDs)
    • 15. URI Overloading
      http://wordnet.princeton.edu/~agraves/wordnet/0.9/
      Owning / Controlling organization
      File directory structure
      Human readable names (ontology and terms)
      Version number
      Unique Identifier
      Web location (URL)
      15
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 16. URI Overloading
      http://wordnet.princeton.edu/~agraves/wordnet/0.9/
      Owning / Controlling organization
      File directory structure
      Human readable names (ontology and terms)
      Version number
      Unique Identifier
      Web location (URL)
      Contributed to SKOS problem. If URIs were only UIDs:
      Non-transitive broader: Create a new resource with new UID
      Transitive broader: change the human readable term name to broaderTransitive, same UID.
      Viola!
      16
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 17. Problems and Root Causes
      17
      Ontology-driven applications break
      Maintenance
      Issues
      Performance Issues
      Overuse of OWL:sameAs
      Proliferation of URIs
      URIs Overloaded
      (especially w/ UIDs)
      Poor change mgmt. infrastructure
    • 18. Change Management Infrastructure
      Inadequate to non-existent
      Stopgap: annotation properties for versioning
      Technologies immature
      Purposely delayed by W3C
      HENCE: no versioning guidelines
      18
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 19. Problems and Root Causes
      19
      Ontology-driven applications break
      Maintenance
      Issues
      Performance Issues
      Semantic infidelity
      Overuse of OWL:sameAs
      Change semantics
      of URIs
      Overloading OWL:sameAs
      Proliferation of URIs
      URIs Overloaded
      (especially w/ UIDs)
      No versioning guidelines
      Poor change mgmt. infrastructure
      Another talk
    • 20. What can be done?
      1. Imagine a future:
      Change management and versioning is solved.
      Specify exactly WHAT that would mean(Don’t worry about HOW)
      Ontology-driven applications are the norm.
      2. Build guidelines that will work in this future.
      20
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 21. Change Management & Versioning Solved
      Unique IDs are separated from URIs/URLs(avoid overloading)
      Automatic tracking and detection of dependencies
      Automatic minting of new UIDs when semantics changes
      Don’t change name if semantics is the same
      Don’t change semantics if name is the same
      21
      Copyright © 2010 Michael Uschold. All rights reserved.
    • 22. SUMMARY: Problems and Root Causes
      22
      Ontology-driven applications break
      Maintenance
      Issues
      Performance Issues
      Semantic infidelity
      Overuse of OWL:sameAs
      Change semantics
      of URIs
      Overloading OWL:sameAs
      Proliferation of URIs
      URIs Overloaded
      (especially w/ UIDs)
      No versioning guidelines
      Poor change mgmt. infrastructure
    • 23. Resources / References
      Ontology Design Patterns Wikihttp://ontologydesignpatterns.org/
      Modeling Issues
      Overloading OWL sameAs
      Proliferation of URIs, Managing Coreference
      Versioning and URIs
      23
      Copyright © 2010 Michael Uschold. All rights reserved.