Sophia: A Flexible, Web-Based Knowledge Server

ONTOLOGIES SPECIFY THE CONcepts and relations within a domain of discourse. Scientists, philosophers, sociologists, and linguistics have been striving for good ontologies since Empedocles described the four elements—air, earth, fire, and water—in the fifth century BC. We now use ontologies for classification, system modeling, humancomputer interaction, computer reasoning, and data mining in fields such as medicine, physics, molecular biology, and electronics. To encourage the development of strong semantic models in science and engineering, developers have created several knowledgerepresentation tools,1,2 including Ontolingua,3 Protégé,4 and Theo.5 Such tools have an array of features, default reasoning strategies, and knowledge-representation constraints. However, some require users to install special software, and others lack important features, such as a persistent backend storage system for scalability, facilities for controlling slot access based on user permissions, an API for prototype development, or easy compatibility with Web protocols. To address these shortcomings, we built Sophia, a Web-accessible ontology and knowledge-base tool built on a common relational database management system (RDBMS). Other knowledge-base systems also use relational or object-oriented databases. For example, the Perk database6 backend to the GKB-Editor and EcoCyc7 framebased knowledge-base tool both use a relational database for storage. The EcoCyc system uses a persistent storage mechanism with a relatively sophisticated caching strategy in which individual frames are stored in a RDBMS as compressed ASCII text and are unpacked and “paged in” on demand into memory. Sophia differs in that it relies on a finer-grained frame representation in the RDBMS and a Structured Query Language (SQL) query mechanism for each retrieval. Sophia is implemented in the RiboWEB8 and MHCWeb9 systems. We’ll describe RiboWEB in more detail in an upcoming issue of IEEE Intelligent Systems. The Sophia system