As a part of the scientific database research underway at the Oregon Graduate Institute, we are collaborating with materials scientists in the research and development of an extensible modeling and computation environment for materials science. Materials scientists are prolific users of computers for scientific research. Modeling techniques and algorithms are well known and refined, and computerized databases of chemical and physical property data abound. However, applications are typically developed in isolation, using information models specifically tailored for the needs of each application. Furthermore, available computerized databases in the form of CDs and on-line information services are still accessed manually by the scientist in an off-line fashion. Thus researchers are repeatedly constructing and populating new custom databases for each application. The goal of our research is to bridge this gulf between applications and sources of data. We believe that object-oriented technology in general and data-bases in particular, provide powerful tools for transparently bridging the gap between programs and data. An object-oriented database that not only manages data generated by user applications, but also provides access to relevant external data sources can be used to bridge this gap. An object-oriented database for materials science data is described that brings together data from heterogeneous non-object-oriented sources and formats, and presents the user with a single, uniform object-oriented schema that transparently integrates these diverse databases. A unique multilevel architecture is presented that provides a mechanism for efficiently accessing both heterogeneous external data sources and new data stored within the database.