International Semantic Web Conference ISWC 2006' Doctoral Consortium Track, Nov 5, 2006 Athens, GA1

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Package-based Description Logics Preliminary
Results

• Jie Bao, Doina Caragea, Vasant Honavar
• Artificial Intelligence Research Laboratory
• Computer Science Department
• Iowa State University Ames, IA USA 50011
• Email baojie_at_cs.iastate.edu

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Outline

• Motivation
• Language Features
• Semantics
• Reasoning
• Applications
• Conclusions

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Modular Ontologies

• What is modular ontology?
• An ontology that contains a set of smaller,
  (semantically) connected component ontologies
• Why modular ontology ?
• A Distributed Semantic Web
• Collaborative Ontology Building (COB)
• Selective Ontology Reuse
• Large Ontology Storage and Reasoning

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A Distributed Semantic Web
Berners-Lee, T., Hendler, J., and Lassila, O.
(2001).The semantic web. Scientific American,
284(5)34-43.
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A COB Example
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Ontology Languages Needed

• Has localized semantics
• Allows distributed reasoning
• Supports fine-grained ontology organizational
  structure
• Allows partial ontology reuse
• Supports selective knowledge hiding
• Enables collaborative and scalable tools

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Modular Ontology Languages Today
2002 2003
2004
2005 2006
DDL based
CTXWL
C-OWL
?
OWL
E-Connections
(E-connection can also work other logics e.g.
modal logic)
(to be discussed at the WoMO workshop)
P-DL
Our approach
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Modular Ontology Languages Today (2)
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Expressivity Comparison
Baot et al. ASWC 2006
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Open problems

• How to obtain stronger expressiveness?
• How to enable distributed reasoning without
  required global knowledge?
• How to ensure the reasoning exactness w.r.t.
  standard reasoning with integrated ontology?
• How to create modular ontologies?

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Outline

• Motivation
• Language Features
• Semantics
• Reasoning
• Applications
• Conclusions

12
Package

• Packages of an ontology
• Are defined in subsets of the same decidable
  DL,e.g., SHOIQ
• May contain both local terms and imported terms
• Each term has a home package
• P Package extension
• PC Package extension with only concept name
  importing
• E.g., SHOIQP SHOIQ P ALCPC ALC PC

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Package Example
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Ongoing work Scope Limitation

• SLM of an ontology term or axiom t
• is a boolean function that defines the visible
  scope of a term or axiom.
• Example SLMs
• Public (t,r) t is accessible from anywhere
• Private (t,r) t is only available in the home
  package

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Outline

• Motivation
• Language Features
• Semantics
• Reasoning
• Applications
• Conclusions

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Localized Semantics
O1
O2
AnimalI
2
AnimalI
DogI
1
2
CarnivoreI
1
DogFoodI
2
PetDogI
DogI
2
PetI
1
2
eatsI
2
x
fooI
2
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Semantics of Importing
AnimalI
2
AnimalI
1
DogI
CarnivoreI
2
1
DogFoodI
2
PetDogI
DogI
2
PetI
1
2
eatsI
2
x
x
fooI
2
Image domain relation
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Global Interpretations

• The (conceptual) global interpretation for the
  (virtually) integrated ontology
• It can be combined from local interpretations

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Partially Overlapped Model
bijective (one-to-one)
Transitive (Compositional consistent)
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P-DL Semantics Features

• Localized Semantics
• Local top concepts are not the same
• Each package explains the world based on its
  transitive importing closure (local point of
  view).
• Stronger expressivity
• Supports both inter-module concept subsumption
  and inter-module role usage.
• Decidable (when all modules are from the same
  decidable DL)
• Solves some reasoning diffculities in other
  approaches

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Outline

• Motivation
• Language Features
• Semantics
• Reasoning
• Applications
• Conclusions

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Reasoning for Modular Ontology

• Major Consideration should not require the
  integration of ontology modules.
• High communication cost
• High local memory cost
• May violate module autonomy, e.g., privacy
• Question can we do reasoning for P-DL without
• (syntactic level) an integrated ontology ?
• (semantic level) a (materialized) global tableau
  ?

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Distributed Reasoning
Stan So they are far from us. Too Bad.
Chef Hello there, children! Where does Kyle
move to?

• Chef
• We are in South Park, Colorado
• San Francisco is in California
• Colorado is far from California.

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Federated Reasoning for P-DL

• Basic strategy
• Use multiple local reasoners, each for a single
  package
• Each local reasoner creates and maintains a local
  tableau based on (only) local knowledge
• A local reasoner may query other reasoners if its
  local knowledge is incomplete
• Global relation among tableaux is created by
  messages

(1)
(4)
(3)
(2)
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ALCPC Expansion Example
L3(x)A??D, ?C?D A,?C, ?D
, ?B

• Messages
• m(x,C) if copy of x has label C
• r(x,C) add C into the label of x (or its copy)
• Message Target Cs home package reasoner

Transitive Subsumption Propagation
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ALCPC Expansion Example (2)
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More complex situations

• Bao Honavar, WI2006
• Cyclic name importing
• Asynchronous parallel reasoning
• Bao etal, (to be submitted)
• Role, nominal importing
• Component languages in SHOIQ

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Ongoing Concealable Reasoning

• A reasoner should not expose hidden knowledge
• However, such hidden knowledge may still be
  (indirectly) used in safe queries.

Yes
Queries
Unknown
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Outline

• Motivation
• Language Features
• Semantics
• Reasoning
• Applications
• Conclusions

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Collaborative Ontology Building

• Ontology modularity facilitates collaborative
  building
• Each package can be independently developed
• Multiple users can concurrently edit the ontology
  on different packages
• Ontology can be only partially loaded
• Unwanted interactions are minimized by limiting
  term and axiom visibility

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The COB Editor
Pig Package
Cattle Package
Chicken Package
http//sourceforge.net/projects/cob/
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WikiOnt 2 (under development)
A Wiki-based Ontology Editor with GUI
Will be on http//sourceforge.net/projects/wikiont
/
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Outline

• Motivation
• Language Features
• Semantics
• Reasoning
• Applications
• Conclusions

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Main Contributions

• Investigate the requirement and formal semantics
  of modular ontologies
• Present a formal modular ontology language, P-DL,
  that can overcome many limitations in existing
  approaches
• Stronger expressivity
• Solve some inference difficulties
• Present a federated reasoning algorithm for P-DL
  that can
• strictly avoid integration of ontology modules
• handle reasoning tasks not solvable in existing
  approaches
• Apply the notion of modular ontology in
  collaborative ontology building

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Ongoing work

• Reasoning with OWL (SHOIQ) Package extension
• Reasoning with selectively hidden knowledge
• The implementation of the distributed reasoner
  (based on Pellet)
• WikiOnt 2

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Publications

• Language Features
• Bao, J. Caragea, D. and Honavar, V. (2006)
  Towards collaborative environments for ontology
  construction and sharing. In International
  Symposium on Collaborative Technologies and
  Systems (CTS 2006). IEEE Press. 99108.
• Semantics
• Bao, J. Caragea, D. and Honavar, V. (2006)
  Modular ontologies - a formal investigation of
  semantics and expressivity. In R. Mizoguchi, Z.
  Shi, and F. Giunchiglia (Eds.) Asian Semantic
  Web Conference 2006, LNCS 4185, 616631.
• Bao, J. Caragea, D. and Honavar, V. (2006) On
  the semantics of linking and importing in modular
  ontologies. In I. Cruz et al. (Eds.) ISWC 2006,
  LNCS 4273. 7286.

http//boole.cs.iastate.edu9090/popeye/Wiki.jsp?p
ageAcademic.Basic.CV.Publication
37
Publications

• Reasoning
• Bao, J. Caragea, D. and Honavar, V. (2006) A
  tableau-based federated reasoning algorithm for
  modular ontologies. 2006 IEEE/WIC/ACM
  International Conference on Web Intelligence (In
  Press).
• Bao, J. Caragea, D. and Honavar, V. (2006) A
  distributed tableau algorithm for package-based
  description logics. In the 2nd International
  Workshop On Context Representation And Reasoning
  (CRR 2006).
• Collaborative Ontology Building
• Bao, J. and Honavar, V. (2004) Collaborative
  ontology building with WikiOnt - a multi-agent
  based ontology building environment. In Proc. of
  3rd International Workshop on Evaluation of
  Ontology-based Tools, at ISWC 2004, pages 3746.
• Bao, J. Hu, Z. Caragea, D. Reecy, J. and
  Honavar, V. (2006) Developing frameworks and
  tools for collaborative building of large
  biological ontologies. In The 4th International
  Workshop on Biological Data Management (BIDM06).
  191-195.

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References (Related Work)

• DDL
• A. Borgida and L. Serafini. Distributed
  description logics Directed domain
  correspondences in federated information sources.
  InCoopIS/DOA/ODBASE, pages 36-53, 2002.
• P. Bouquet, F. Giunchiglia, and F. van Harmelen.
  C-OWL Contextualizing ontologies. In Second
  International Semantic Web Conference, volume
  2870 of Lecture Notes in Computer Science, pages
  164-179. Springer Verlag, 2003.
• L. Serafini, A. Borgida, and A. Tamilin. Aspects
  of distributed and modular ontology reasoning. In
  IJCAI, pages 570-575, 2005
• L. Serafini and A. Tamilin. Local tableaux for
  reasoning in distributed description logics. In
  Description Logics Workshop 2004, CEUR-WS Vol
  104, 2004.
• L. Serafini and A. Tamilin. Drago Distributed
  reasoning architecture for the semantic web. In
  ESWC, pages 361-376, 2005.
• E-Connections
• B. C. Grau. Combination and Integration of
  Ontologies on the Semantic Web. PhD thesis, Dpto.
  de Informatica, Universitat de Valencia, Spain,
  2005.
• O. Kutz, C. Lutz, F. Wolter, and M.
  Zakharyaschev. E-connections of abstract
  description systems. Artif. Intell., 156(1)1-73,
  2004.

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• Thanks!

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SLM example
Package
Package Hierarchy

Scope Limitation
A schedule ontology
Visible there is an activity
Hidden details of the activity
CTS06 Paper a.k.a 1
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DL Interpretation - Example
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Messages
y
y
T1
T2
C?
C(y)
y
y
T1
T2
C
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Tableau Expansion
Tableau Expansion for ALCPC with acyclic concept
importing
More expressive extensions in action SHOIQ P