In this appendix, we illustrate the idea of an ontology description with a concrete example. In the digital library, ontologies provide the mechanism whereby information agents with divergent implementations (e.g., because they were developed by separate organizations) or with varying domains of expertise can nevertheless communicate in mutually understandable terms.
This particular example is taken from our prior work in distributed configuration design, where catalog agents representing distinct manufacturers or design teams coordinate on the design of a complex device. The role of the ontology in this domain is to specify precisely what the problem is, so that the particular constructs employed by the individual agents can be translated into the common framework. In the description below, italicized terms correspond to distinguished onto logical entities. The language employed is semi-formal English; in the actual computational version we use a formal ontology language based on first-order logic. This example is given merely to illustrate the use of ontology for coordination: the ontologies developed for the digital library will differ substantially in form and content.
The ontology captures a standard framework for configuration design. We start by defining what it means to specify a design problem, and give formal definitions for the terms used in describing a design.
Configuration design is a process of selecting parts to perform functions. More precisely, a design problem consists of:
Given this design ontology, implementors of design agents can precisely characterize the behavior of their modules, and the conditions for interaction with other agents. Developers of distributed design algorithms can specify their protocols using this common high-level terminology, without requiring that the participating agents be homogeneous at lower levels of detail.
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