Dynamic Ontologies on the Web Jeff Heflin, James Hendler

Motivation of SHOE The World Wide Web is mostly inaccessible to machines No facilities for formalizing the meaning of web languages An XML syntax is not sufficient for traditional KR The dynamic and distributed nature of the Web

Overview of SHOE Extends HTML with a set of knowledge oriented tags Associates meaning by making each web page commit to ontologies Defined as an application of SGML to achieve compatibility with existing web standards Its simplicity makes it easy for users to understand and tool developers to implement It is possible to develop numerous tools and architecture for processing

Language Features of SHOE SHOE ontologies build on or extend other ontologies, inherit all of the components present in their ancestors (interoperable) Extending general ontologies to create more specific ontologies. (reuse) An ontology can define categories, relations, and other components with corresponding tags It can specify a local name for a concept from other extended ontology

Language Features of SHOE (cont) SHOE uses inference rules which consists of a body and a head consisting of one or more subclauses ( and ) Three subclauses: category relation comparison

Mapping SHOE to FOL Horn clause

Mapping SHOE to FOL (cont) A formula F is well-formed with respect to O if : 1) F is an atom of the form p(t1,…,tn) where p is a n-ary predicate symbol such that p  V 2) F is a Horn clause An ontology is well-formed if every axiom in the ontology is well-formed with respect to the ontology

Mapping SHOE to FOL (cont) Introduces a perspective P= as a data source S= viewed in the context of O= Let Ws be the subset of Ds that is well- formed with respect to O, then P results will be T=Ws  A

The necessity of revision Previous assumptions: static or isolation environment changes without side effects The changes of ontologies correct errors accommodate new information adjust the representation of a particular domain

Effects of revisions Removal of categories or relations from original ontology may result in fewer answers to a given query Addition of categories or relations can maintain the same perspective on all legacy data sources

Versioning of SHOE Copies the original ontology file, assigns it a new version number, and adds or removes elements as needed It can specify that it is compatible with previous versions Be cautious of malicious revisions

Ontology Integration It is inevitable that new concepts will be defined while existing ones still can be used Four types of domain differences: Terminology Scope Encoding context OI typically involves identifying the correspondence between two ontologies, determining the differences in definitions, and creating a new ontology that resolves these differences.

Three suggested ways to incorporate the results of OI

Related work Ontobroker (Fensel et al. 1998) OML and CKML (Kent 1999) RDF Ontolingua Server

Conclusions Pros 1. Analyzes the problems of ontologies in a dynamic, distributed and heterogeneous environment 2. Be compatible with existing web standards 3. Simplicity of SHOE 4. Prevent logical inconsistency Cons 1. Disjunction? 2. Class hierarchy?