We have rich information resources for materials science and engineering - raw measurement data, computational simulation methods, digitized handbooks, and digital libraries. However, these resources have a wide variety of formats, terminologies, and concepts, which makes it difficult to find appropriate information for materials design, development, and evaluation. One solution to this problem is to integrate these resources into a computer readable concept map, called a domain ontology, which describes concepts and relationships among the concepts in materials science and engineering. This paper describes a trial that constructs a standard of metadata description using ontology language and demonstrates the validity of this construction through data exchange among heterogeneous material databases. "Materials Ontology," which consists of several sub ontologies corresponding to substance, process, environment, and property, is developed using the ontology language of the Semantic Web, OWL, which enables the definition of a flexible and detailed structure of materials information. A versatile "materials data format" is built on the Materials Ontology as a component of the materials information platform and is applied to exchange data among three different thermal property databases, maintained by two major materials science research institutes in Japan.