Artificial Intelligence Research LaboratoryComputational Intelligence, Learning, and Discovery ProgramDepartment of Computer Science, Iowa State University

Modular Ontologies: the Package-based Description Logics Approach

Acknowledgements: This research was supported in part by a grant from the US National Science Foundation (IIS-0639230) and support from the USDA Bioinformatics Coordination Project.

Jie Bao and Vasant Honavar

ABSTRACTModularity in ontologies is required in many application scenarios, such as collaborative ontology building, partial ontology reuse, selective knowledge hiding, and distributed data management. Consequently, there is an urgent need for ontology languages with features such as localized semantics, partial reusability, well-structured organization and flexible knowledge scope limitation. This study will investigate a new modular ontology language, Package-based Description Logics (P-DL). In P-DL, an ontology is composed of a collection of modules called packages. Different from existing modular ontology language proposals that adopt the “linking” approach, P-DL adopts a selective “importing” mechanism to create semantic connections between ontology modules. The semantics of P-DL relaxes the strong local domain disjointness adopted in existing approaches. Consequently, P-DL has stronger expressivity and overcomes many semantic difficulties presented in existing approaches. This poster will present preliminary results on the syntax, semantics, and the reasoning algorithm of P-DL ontologies.

1 – Construction of a Non-Redundant Dataset of RNA-Binding Proteins

SUMMARY

We present an expressive module ontology language, Package-based Description Logics (P-DL) Semantics of P-DL allows local models of ontology modules to be partially overlapping thus solves many problems presented in existing approaches. We give a federated reasoning algorithm for P-DL that can do inference without a global semantics, thus also avoids ( usually costly) ontology integration.

2 – P-DL Features

1 – Motivation

3 – Reasoning with P-DL

P-DL Semantics: • Each package has a local model (a possible world that conforms the logic of the package)• Local models may be partially overlapping• Solves problems in existing proposals, e.g., expressivity limitations, modules transitive reusability, inter-module unsatisfiability.

REFERENCES

J. Bao, D. Caragea, and V. Honavar. (2006) On the Semantics of Linking and Importing in Modular Ontologies. accepted by the International Semantic Web Conference (ISWC) 2006. J. Bao, D. Caragea, and V. Honavar. (2006) Modular ontologies - a formal investigation of semantics and expressivity. 2006. In the Asian Semantic Web Conference (ASWC2006) (In Press). J. Bao, D. Caragea, and V. Honavar. (2006) A distributed tableau algorithm for package-based description logics. In the 2nd International Workshop On Context Representation And Reasoning (CRR 2006) (In Press). 2006. J. Bao, D. Caragea, and V. Honavar. (2006) Towards collaborative environments for ontology construction and sharing. In International Symposium on Collaborative Technologies and Systems (CTS 2006). 2006.

Ontology:• (formally) shared specification of conceptualization• (Informally) a term set and relations between termsModular Ontology:• An ontology that consists of multiple modules

Aug 17, 2006

Swine

CattleChicken

Horse

Each group works on an ontology module for a particular species (according to the group’s best expertise)

Collaborative building of an animal trait ontology that involves multiple research groups across the world

Fig 1: Modular Ontology Application Example: Collaborative Ontology Building

Limitations in existing ontology languages:• No support for localized semantics – reasoning only with a single ontology • Reuse all or nothing of an ontology• Do not allow fine-grained organizational structure• Do not allow partial knowledge hiding – everything is “public”•Result in unstructured, hard-to-build, hard-to-reuse, intractable ontologies!

P3

protected

1. Whole ontology consists of a set of packages

2. Packages are organized in hierarchies

3. Terms and axioms are defined in packages with scope limitations

P1

P2

public

private

P1

P2

public

private

General Pet

Wild Livestock

Animal ontology

PetDogPet

DogGeneral

O1 (General Animal) O2 (Pet)

P-DL: Package-based Description Logics, a modular ontology language that has the following features:

Fig 2: P-DL Features

Fig 3: (a) Whole ontology consists of a set of packages, one package can import terms from another package (b) A concrete example given in P-DL (arrows indicate importing relations)

(a) (b)

General

Pet

Dog

Animal ontology•A nested package is a part of another package•Could be used to represent the organizational structure of an ontology

•Arrange knowledge•Enforce hierarchical management of knowledge

Packages

Package Hierarchy

Fig 4: Package Hierarchy

Scope Limitation

• Scope Limitation Modifier (SLM) defines the visible scope of a term or axiom • Eg. Public, Private, Protected

x x’

ΔI1 ΔI2

CI1 CI2

r12

ΔI3

r13 r23

x’’

CI3

x

CI

(a) (b)

Fig 5: (a) There are local models for each package that are connected by “domain relations” (arrows in figure); (b) A global model can be obtained from those partially overlapping local models

x1

{A1,B1}

{A2}

{A3,B3}

{B2}x2 x3

x4

x1

{A1}

{A2}

{A3}

x2

x4

x1

{B1}

{B3}

{B2}x3

x4

The (conceptual) global tableau Local Reasoner

for package ALocal Reasonerfor package B

Fig 6: Reasoning with P-DL. There are multiple local reasoners each for one package. Each local reasoner maintains a local tableau which is a “projection” of the global tableau. Connections between local tableaux is created by a set of messages.

Reasoning with P-DL: constructing a (virtual) global model (represented by a “tableau” tree in the reasoning algorithm) by constructing multiple local tableaux using a federation of local reasoners.