Role of Ontologies in OSF

Ontologies are the structures that control the Open Semantic Framework. Ontologies are, in essence, graph structures. Graphs are among the most ubiquitous models of both natural and human-made systems. They can be used to model many types of relations and process dynamics in physical, biological and social systems. Any problem of practical interest may be represented by a graph. Ontologies are one such graph structure for representing various knowledge domains.

A graph is an abstract representation of a set of objects where pairs of the objects are connected. The objects are most often known as nodes or vertices; the connections between the objects are called edges. Typically, a graph is depicted in diagrammatic form as a set of dots or bubbles for the nodes, joined by lines or curves for the edges. If there is a logical relationship between connected nodes the edge is directed, and the graph is known as a directed graph. Various structures or topologies can be expressed through this conceptual graph framework.

Ontologies are the graph frameworks for organizing information on the semantic Web and within semantic enterprises. They provide unique benefits in discovery, flexible access, and information integration due to their inherent connectedness; that is, their ability to represent conceptual relationships. Ontologies can be layered on top of existing information assets, which means they are an enhancement and not a displacement for prior investments. And ontologies may be developed and matured incrementally, which means their adoption may be cost-effective as benefits become evident.

In the Resource Description Framework (RDF) model, the nodes can represent “nouns” or subjects or objects (depending on the direction of the links) or attributes. The edges or connections represent “verbs” or relationships, properties or predicates. Thus, the simple “triple” of the basic statement in RDF (consisting of subject – predicate – object) is one of the constituent barbells that make up what becomes the eventual graph structure.

Ontologies are essentially a series of these connected statements. Each statement relates a "thing" to either another thing or to a value for an attribute. The object of one assertion can be the subject of another one. In this manner, these triples get connected together to form the graph structure of a knowledge ontology.



As used within the Open Semantic Framework, these ontologies thus become a schema definition for the relation of various things within the applicable knowledge domain. Through this graph structure, it is possible to find and trace and relate the relationships of things. If these connections and relationships make sense — that is, if the ontology is coherent — then there is a consistent logic model for searching and organizing information within the domain.

At a true schema level (known as a TBox in description logics, the logic basis for the OWL ontologies used by OSF), ontologies represent the concept and relationships of the domain at hand. These ontologies also host the specific local entities and prominent things (people, places, events, etc., also known as the ABox) useful for extracting local and domain-specific relevance.

This concept level represents the “world view” of the specific instantiation of a given OSF installation. This conceptual (TBox) view provides the structural organization of information, inferencing capabilities, and navigation, faceting and explorer structure. The entity (ABox) view provides tagging for prominent individuals and instances important to the domain, and guides the structure behind data visualizations of attribute or indicator data.

In addition to this knowledge domain purpose, ontologies are also used for guiding how the various applications work within an OSF installation. These supplementary administrative ontologies guide, for example, how the user interfaces or widgets in the system should behave. This design approach in OSF combining domain and administrative ontologies as a way to specify the scope and behavior of the system is known as ODapps, for ontology-driven applications.

The administrative level uses simple roles and relationships for attributes and indicators to inform the framework as to how and with what widget to display information. For example, a “type” of information that is geographically related can be instructed to use the map component as an option for display. Whether some information is used for totals, comparison purposes, or other specifications useful to data visualization and graphing may also be specified.

The language and relationships (predicates or properties) of these administrative ontologies are simple and straightforward. It is, for example, relatively easy to define data display functions at the broad dataset and attributes level. Simple determinations drive how results sets and their associated results types may be displayed, no matter what datasets or slices may be generated as a result of the queries or requests fed to the system.

The structure in these layers can be replaced by other structures for other instantiations and circumstances. Indeed, all layers in the Open Semantic Framework can remain relatively fixed while tailoring the instance to new domains solely via the ontologies employed. Ontologies are what provides any given instantiation of OSF its unique focus and scope.