  In the materials design domain, much of the data from materials calculations
are stored in different heterogeneous databases. Materials databases usually
have different data models. Therefore, the users have to face the challenges to
find the data from adequate sources and integrate data from multiple sources.
Ontologies and ontology-based techniques can address such problems as the
formal representation of domain knowledge can make data more available and
interoperable among different systems. In this paper, we introduce the
Materials Design Ontology (MDO), which defines concepts and relations to cover
knowledge in the field of materials design. MDO is designed using domain
knowledge in materials science (especially in solid-state physics), and is
guided by the data from several databases in the materials design field. We
show the application of the MDO to materials data retrieved from well-known
materials databases.
