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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 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, 20061


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Outline

  • Why Modular Ontology

  • Evolution of Modular Ontologies

  • Local Domain disjointness

  • Conclusion

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 20062


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Local Points of View

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 20063


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Messy “Spaghetti” Ontologies

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 20064


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When load a large ontology…

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 20065


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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, 20066


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Outline

  • Why Modular Ontology

  • Evolution of Modular Ontologies

  • Local Domain disjointness

  • Conclusion

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 20067


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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, 20068


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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, 20069


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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, 200610


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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, 200611


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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, 200612


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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, 200613


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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, 200614


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Outline

  • Why Modular Ontology

  • Evolution of Modular Ontologies

  • Local Domain disjointness

  • Conclusion

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 200615


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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, 200616


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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, 200617


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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, 200618


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DDL Inter-module Unsatisfiability Problem

Flym1

Bird onto Penguin

Penguinm2

Birdm1

~Fly onto Penguin

[Grau, 2005]

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 200619


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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, 200620


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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, 200621


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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, 200622


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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, 200623


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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, 200624


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Outline

  • Why Modular Ontology

  • Evolution of Modular Ontologies

  • Local Domain disjointness

  • Conclusion

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 200625


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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, 200626


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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, 200627


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Thanks!

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 200628


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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, 200629


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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, 200630


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SE was miserable, too

  • Until fine-grained organization is introduced:

Semantic structure

Organizational structure

WoMo 2006 @ ISWC, Athens, GA USA. Nov 5, 200631


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