A data warehouse is a conceptual repository that collects information from one or more data sources and provides a schema that allows this repository to be queried by users of the warehouse. The difficulties in designing a schema for a data warehouse whose member databases are multimedia databases are mainly caused by the highly diverse nature of multimedia data, a very wide range of multimedia requirements, and the heterogeneous schemas of the member databases. In this paper, two possible models for the schema of a data warehouse composed of multimedia database systems - the Markov Model Mediator (MMM) mechanism and an object-oriented data model - are compared based on some design issues. The comparative analysis shows that the proposed MMM mechanism provides a better schema for a data warehouse than an object-oriented data model.