We describe the design of an object-oriented multimedia database management system that can store and manage SGML/HyTime compliant multimedia documents. The system is capable of storing, within one database, different types of documents by accommodating multiple document type definitions (DTDs). This is accomplished by dynamically creating object types according to element definitions in each DTD. The system also has tools to automatically insert marked-up documents into the database. We discuss the system architecture, design issues and the system features.