This paper presents the Ontology for Accessing Transcription Systems (OATS), a knowledge base that supports interoperation over disparate transcription systems
and practical orthographies. The knowledge base includes an ontological description of writing systems and relations for mapping transcription system segments to an interlingua pivot, the IPA. It includes orthographic and phonemic inventories from 203 African languages. OATS is motivated by the desire to query data in the knowledge base via IPA or native orthography, and for error checking of digitized data and conversion between transcription systems. The model in this paper implements these goals.