Computer music environments (CMEs) are notoriously difficult to design and implement. As computer programs, they reflect the complex nature of music ontology and must support real-time manipulation of multimedia data. In addition, these programs must be usable by native users, supporting their creative process without obstructing it through technical difficulties. To achieve these goals, the authors argue, CMEs must be provided with a well-defined methodology relying on techniques from the fields of software engineering, artificial intelligence, and knowledge representation. This paper contributes an aspect of this methodology, concentrating on the role of visualizations in CMEs. The authors state that visualization deserves a specialized theory that is based on music ontology and that is independent of the concrete, implemented graphical interface.