Issues in Ontology-based

Information integration

By Zhan Cui, Dean Jones and Paul O’Brien

E-commerce

Requirement:

• Retrieve and Integrate information from multiple resources.

• Details of the resources are hided from users.

Obstacles:

• Understand queries.

• Determine resources.

• Integrate information.

Four levels in interoperability problems

1. System level: incompatible hardware and operating system.

2. Syntactic level: different language and data representations.

3. Structural level: different data models.

4. Semantic level: the meaning of terms.

e.g., synonyms.

Many technologies address problems in first three levels, such as CORBA, DCOM, etc.

XML vs. Semantic Heterogeneity Problems

XML:

• Can solve problems in schema level.

• Provide common syntax for exchanging heterogeneity information.

• Some standards for e-commerce:

e.g., ebXML.

XML:

• Cannot solve problems in semantic level.

• Terminology may not consistent in one file or in a set of files.

Solution

• Formally specify the meaning of the terminology of each system

(Formal ontology)

• Define a translation between each system terminologies and an intermediate terminology.

(Ontology mapping)

Outline

• Issues in Resolving Semantic Heterogeneity

• Description of DOME

• DOME Demonstrator

• Conclusion

Issues in Resolving Semantic Heterogeneity

--- Developing ontologies

Formal ontology:

• A formal ontology consists of definitions of terms.

• It usually includes concepts with associated attributes, relationships and constraints defined between the concepts and instances of concepts.

Formal ontologies include different type of ontologies for different purposes:

• Resource ontologies: define the terminology used by specific information resources.

• Personal ontologies: define the terminology of a user or some group of users.

• Shared ontologies: the common terminology between a number of different systems.

Issues in Resolving Semantic Heterogeneity

--- Developing ontologies

The best approach to develop ontologies is usually determined by the eventual purpose of the ontologies.

For example:

•Resource ontologies: bottom-up approach.

•Shared ontologies: top-bottom approach.

Issues in Resolving Semantic Heterogeneity

--- Mapping Between Ontologies

•Human intervention is necessary.

•Some tools are helpful: mediator systems, mapping libraries and conversion functions.

•Mapping is not accurate. Information could be lost. This is unacceptable for e-commerce.

Issues in Resolving Semantic Heterogeneity

--- Ontologies and Resource Information

• How to choose resources?

• It is necessary for resources to describe themselves: resource ontologies.

• Personal ontologies are important for the system to understand queries exactly.

• Many issues in locating resources:

e.g., users prefer one resource over another;

Issues in Resolving Semantic Heterogeneity

--- Ontologies and Database Schemas

Schema vs. Ontology

The main difference is their purposes.

• A schema is developed in order to model some data.

• A ontology is developed to define the meaning of the terms.

A resource has a formal ontology. Data are store in database based on schema. Mapping between formal ontology and resource schema is necessary.

Issues in Resolving Semantic Heterogeneity

--- Entity Correspondence

• There may be a lot of resources related to one query.

• Information have to be integrated to answer query.

• Construct correspondence between entities across resources.

• Key attributes can be used to build correspondence.

• It is hard to determine whether information from different resources is same or not.

DOEM Overview

• Ontology-based techniques.

• Designed for data reuse and knowledge sharing.

• Retrieve information from multiple resources to answer queries.

• Present results in a consistent way.

DOEM (Domain ontology Management Environment)

The DOEM architecture

DOEM Overview

• Develop and administrate a DOEM system.

• Extract (semi-automated) ontologies from legacy system to define ontologies and mappings.

• Allow engineers to select best developing approach: top-down or bottom-up.

• Engineers: define mapping between resource ontologies and shared ontologies, resources and shared ontologies, database schemas and resource ontologies.

--- Engineering client

DOEM Overview

• Store ontologies defined using the engineering client.

• Allow user to access: share ontologies, resource ontologies, application ontologies.

• Access through OKBC interface.

• Implement ontologies using the description logic CLASSIC which can store ontologies and make inference.

--- Ontology server

DOEM Overview

• Interface to access system.

• Query information space.

• Load and browse ontologies.

• Queries and results use the same terminology.

--- User client

DOEM Overview

• Store mappings between ontologies.

• Store generic conversion functions.

• Use a declarative syntax.

• Can be queried by query engine.

--- Mapping server

DOEM Overview

• Most interaction between a resource and the DOME network occurs via wrappers.

• Translate queries between DOME and resources.

• Translate information that will be put into the terminology of the particular resource.

--- Wrappers

DOEM Overview

• Let system know which resources are available and what these resources are.

• Store the directories and descriptions of resources.

--- Resource Directory

• Obtain a list of currently available and relevant resources from resource directory.

• Decompose the query into sub-queries.

• Send the sub-queries to the resources.

• Translate queries from the ontology of the query to that of the relevant resource.

• Integrate results.

DOEM Overview

--- Query engine

The DOEM architecture

DOME Demonstrator

• Based on a database of marketing scenario.

• DOME controls mapping and limits resources.

Conclusions

• Solve information query at semantic level with formal ontologies and ontology mappings.

• Provide an integrated view of networked heterogeneous databases.

• Allow a user to select and browse definitions of terminologies.

DOME:

Comments

• General description.

• There is no details and experiments.

• No new technique is introduced.