In the materials design domain, much of the data from materials calculations is stored in different heterogeneous databases with different data and access models. Therefore, integrating data from different sources is challenging. As ontology-based access and integration alleviate such issues, we developed the Materials Design Ontology (MDO) for increasing interoperability among computational materials databases. Then, the team introduced a generic framework (OBG-gen) for using GraphQL in which a global domain ontology informs the generation of a GraphQL server that answers requests by querying heterogeneous data sources. By using MDO in this framework, it is possible to generate a GraphQL server for data integration among heterogeneous computational materials databases. Additionally, the team introduced a method (ToPMine-FTCA) for ontology extension and applied it in the materials science domain.