Companies suer from heterogeneous data sources that are distributed across all business units and locations. Accessing, discovering, and understanding these data sources is challenging because data scientists have to deal with dierent protocols, data formats, and even company-specic organizational issues such as rewalls and privacy policies. Ontology-Based Data Management (OBDM) provides dierent aspects for reducing the barriers of integrating, accessing and managing heterogeneous data sources by using ontologies. For that, we establish a mapping between data sources and one or multiple target ontologies. However, the biggest challenges in ODBM are creation and administration of required ontologies. Usually, these ontologies are created in advance, for instance, by ontology engineers and domain experts that closely work together for manually designing and even maintaining the ontology. In order to enhance the process of designing and maintaining an ontology, we propose an approach consisting of an evolving knowledge graph that includes an internal ontology, which continuously evolves on demand as domain experts add new data sources and dene the mapping between the ontology and that data source. For this purpose, we develop an intuitive, user-oriented wizard and combine it with a semi-supervised evolution strategy that supports the user with the help of external knowledge databases. Moreover, we equip the system with additional logic that allows to automatically link related concepts of the ontology. We evaluate the accuracy and usability of our approach by conducting a user 20 André Pomp et al. study. The results show that mappings become more objective and consistent with our provided user wizard, resulting in a knowledge graph with higher connectivity and stability.