Excerpts from Ontology Building: A Survey of Editing Tools:

With databases virtually all of the semantic content has to be captured in the application logic. Ontologies, however, are often able to provide an objective specification of domain information by representing a consensual agreement on the concepts and relations characterizing the way knowledge in that domain is expressed.

All ontologies have a part that historically has been called the terminological component. This is roughly analogous to what we know as the schema for a relational database or XML document. It defines the terms and structure of the ontology’s area of interest. The second part, the assertional component, populates the ontology further with instances or individuals that manifest that terminological definition. This extension can be separated in implementation from the ontology and maintained as a knowledge base.

CL – Common Logic is the emerging successor to the KIF ontology construction language.

The wide array of information residing on the Web has given ontology use an impetus, and ontology languages increasingly rely on W3C technologies like RDF Schema as a language layer, XML Schema for data typing, and RDF to assert data.

…tools, like Microsoft’s Visio for Enterprise Architects, use an object-oriented specification language to model an information domain (in this case, the Object Role Modeling language). These tools presently lack useful export capabilities, although independent tools to convert between UML and ontology languages like DAML+OIL are under development.

Methodology…in today’s tools…explicit support for a particular knowledge engineering methodology (like KADS) is not common.

Interoperability…Ontologies are for sharing…One consideration in the enterprise realm, for example, is the ability of a domain ontology to accommodate specialized XML languages and controlled vocabularies being adopted as standards in various industries. None of the current ontology editors address this capability. Interoperability, instead, is being addressed simply through an editor’s ability to import and export ontologies in different language serializations.

Usability…The standard approach is the use of multiple tree views with expanding and contracting levels. A graph presentation is less common, although it can be quite useful for actual ontology editing functions that change concepts and relations. The more effective graph views provide local magnification to facilitate browsing ontologies of any appreciable size. The hyperbolic viewer included with the Applied Semantics product, for example, magnifies the center of focus on the graph of concepts (without labeled relations). Other approaches like the Jambalaya plug-in for Protégé-2000 achieve a kind of graphical zooming that nests child concepts inside their parents and allow the user to follow relations by jumping to related concepts. Some practitioners however, such as GALEN users, indicate a preference for non-graphic views for complex ontologies.