Avoiding a Semantic Web Roadblock: URI Management and Ontology Evolution
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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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Avoiding a Semantic Web Roadblock: URI Management and Ontology Evolution Presentation Transcript

  • 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.