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 r esource 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)

DOEM Overview Ontology server: manage the definitions of terms. Mapping server: manage the relationships between ontologies. Engineering client: develop and administrate a DOEM system. User client: support querying. Query engine: decompose queries to sub-queries.

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.