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Divide and Conquer Semantic Web with Modular Ontologies - A Brief Review of Modular Ontology Language Formalisms

Divide and Conquer Semantic Web with Modular Ontologies - A Brief Review of Modular Ontology Language Formalisms Jie Bao and Vasant Honavar Artificial Intelligence Research Laboratory, Department of Computer Science, Iowa State University, Ames, IA 50011-1040, USA.

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Divide and Conquer Semantic Web with Modular Ontologies - A Brief Review of Modular Ontology Language Formalisms

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  1. Divide and Conquer Semantic Web with ModularOntologies - A Brief Review of Modular OntologyLanguage Formalisms Jie Baoand Vasant Honavar Artificial Intelligence Research Laboratory, Department of Computer Science, Iowa State University, Ames, IA 50011-1040, USA. {baojie, honavar}@cs.iastate.edu First International Workshop on Modular Ontologies (WoMo2006), co-located with ISWC 2006 WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 1

  2. Outline • Why Modular Ontology • Evolution of Modular Ontologies • Local Domain disjointness • Conclusion WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 2

  3. Local Points of View WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 3

  4. Messy “Spaghetti” Ontologies WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 4

  5. When load a large ontology… WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 5

  6. So we may need An ontology language that has the support for • Localized semantics • Fine-grained organization. • Partial use/reuse Some more desirable features • Collaborative ontology building. • Distributed reasoning In short: a modular ontology language WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 6

  7. Outline • Why Modular Ontology • Evolution of Modular Ontologies • Local Domain disjointness • Conclusion WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 7

  8. Timeline 1998 2002 2003 2004 2005 2006 CTXML C-OWL DFOL DDL Role<->Concept Mapping P-DL OWL ? (One purpose of the workshop) CЄ(SHOIN(D)) E-Connections CЄ(SHIF(D)) IHN+s WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 8

  9. Pre Semantic Web (1) • Cyc micro-theory [Lenat. Commun. ACM,1995] • The collections of concepts and facts pertaining to particular knowledge domains • Partition based Logics [Amir & McIlraith. KR 2000] • automatically decompose propositional and first-order logic (FOL) into partitions • an algorithm for reasoning with such partitions using message passing. WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 9

  10. Pre Semantic Web (2) • Local Model Semantics [Giunchiglia & Ghidini. KR 1998] • Distributed First-Order Logic [Ghidini & Serafini. 1998] Locality + Compatibility WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 10

  11. DDL • Distributed Description Logics [Borgida & Serafini CoopIS 2002] • Syntax: CTXML [Bouquet etal. MeaN 2002], C-OWL [Bouquet et al. ISWC 2003] • Extensions: Role-concept mapping [Ghidini & Serafini, ESWC 2006], role-role mapping [Ghidini & Serafini, WOMO 2006] WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 11

  12. E-connections • E-connections [Kutz etal. KR 2002] [Grau et al. ISWC 2004] [Grau, Dissertation 2005] • More role constructors • Generalized link [Parsia & Grau, AAAI 2005] WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 12

  13. P-DL • Package-based Description Logics [Bao et al, CTS 2006, ASWC 2006, ISWC 2006] • An importing approach WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 13

  14. More Recent Proposals • Semantic Importing [Pan etal. WOMO 2006] • Allow both syntatical importing (owl:imports) and semantic importing (owl:semanticImports) • Local Ontologies [Grau etal, KR 2006] [Grau & Horrocks IJCAI 2007] • Restrict axioms to be “local”, i.e., has no global effect, i.e. no axiom should define “T”(top) • Local ontologies are conservative extension to each other (i.e. no new knowledge over old module): • O1 U O2 |= a <-> O2 |= a (a is a formula in O2) WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 14

  15. Outline • Why Modular Ontology • Evolution of Modular Ontologies • Local Domain disjointness • Conclusion WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 15

  16. Disjoint Local Domains • Implicit domain disjointness – DDL • domain relations do not indicate individual identity • even if two individuals 1 : x and 2 : x are the same object, they are still treated as if they are different individuals • Explicit domain disjointness – E-Connections • "The general idea behind E-Connections is that the interpretation domains of the connected knowledge bases (…) are kept disjoint and interconnected by means of link relations…” [Grau, 2005] WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 16

  17. Δ Δ friendOf neighbourOf r13 r13 1 3 Domain Relations Disjoint local domains (DDL and E-connections) WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 17

  18. DDL :Subsumption Propagation Problem DDL domain relations are not transitively reusable (without extra restrictions) Cm1 Dm2 C into D C into E ? D into E Em3 [Grau, 2005] WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 18

  19. DDL Inter-module Unsatisfiability Problem Flym1 Bird onto Penguin Penguinm2 Birdm1 ~Fly onto Penguin [Grau, 2005] WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 19

  20. Why? • Bridge rules can be seen as special roles • For a role to simulate subsumption, it should preserve some properties of subsumption • e.g. Transitive (globally reusable) , non-empty, transfer (un)satisfability • Arbitrary bridge rule semantics leads to problems • Better to prevent those problems with a more normative semantics WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 20

  21. E-Connections: Expressiveness Problems • A class cannot be declared in an ontology as a subclass of a foreign class; • A property cannot be declared as sub-relation of a foreign property; • An individual cannot be declared as an instance of a foreign class • A pair of individuals cannot instantiate a foreign property; • The combined use of E-Connections and owl:imports raises a number of difficulties. [Grau, Dissertation 2005] WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 21

  22. r12 P-DL: Partially Overlapped Domains ΔI1 ΔI2 x’ x CI2 CI1 x r13 r23 CI x’’ CI3 Global model obtained from local models by merging shared individuals ΔI3 WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 22

  23. Why Partially Overlapped ? • Ensure a term is always explained the same across multiple modules • Does not mean the loss of local point of view • “I know what your means, but I still don’t agree with you” • Ensure reasoning exactness • Satisfability transfer: “copies of possible things are also possible” • Ensure knowledge is transitively reusable • “Since everybody knows Apple has only one meaning, we can use it regardless where you hear it from” WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 23

  24. Why Partially Overlapped ? (2) • Reasoning support • Possible for very expressive P-DL: SHIQP • Nominals “O” may also be allowed (nominals are in the shared local domain). • Allows federated reasoning: • Peer reasoners with access only to local knowledge • Global knowledge discovered via messages • Compatible to OWL syntax • Only needs to redefine owl:imports • Maximal tool backwards compatibility WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 24

  25. Outline • Why Modular Ontology • Evolution of Modular Ontologies • Local Domain disjointness • Conclusion WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 25

  26. Modular Ontologies Today • Has several approaches to support localized semantics • Several syntax extensions to OWL • Tools available for limited reasoning and editing supports: DRAGO, Pellet, Swoop, COB-Editor • Several methods to decompose large ontologies into modules. WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 26

  27. Open Problems • What modular ontologies are safe and robustly decidable? • Complexity of expressive modular ontologies. • A community-wide accepted, OWL-compatible syntax for expressive modular ontologies. • Highly optimized, truly distributed reasoner • optimized on caching, parallel searching, reasoning on grid • Integration with p2p systems • Collaborative ontology building with modularity. WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 27

  28. Thanks! WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 28

  29. Miserable Life in Ontology Eng. • OpenCyc, only a small portion of the Cyc KB, needs 9 hours to load into Protégé. • Protege crashes when I try to open Wordnet ontology. • I really wants to reuse Grape knowledge in the Food ontology, but can not do it without accepting all other “junk” in the it. • My ontology is small, but a reasoning request is unbelievably slow, just because it imports one big ontology • When I submit a single-word change to the Gene ontology, the GO CVS duplicates the entire ontology. • And it is overwritten by somebody the next day! WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 29

  30. Happy Life in Software Eng. • Highly organized program structure • Mature methods to build large programs • Scalable building, debugging, running of applications • Collaborative software building by modules • Controllable interactions between modules. WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 30

  31. SE was miserable, too • Until fine-grained organization is introduced: Semantic structure Organizational structure WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 2006 31

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