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 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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  • 2Maintenance issues increase chance of mistakes which breaks applications.
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  • Avoiding a Semantic Web Roadblock: URI Management and Ontology Evolution

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

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