The Virtual Knowledge Graph (VKG) approach, also known in the literature as Ontology-Based Data Access (OBDA) [8,12], has become a popular paradigm for accessing and integrating data sources . In such approach, the data sources, which are normally relational databases, are virtualized through a mapping and an ontology, and presented as a unified knowledge graph, which can be queried by end-users through a vocabulary they are familiar with. At query time, a VKG system translates user queries over the ontology to SQL queries over the database. This approach frees end-users from the low-level details of data organization, so that they can concentrate on their high-level tasks. As it is gaining more importance, the VKG paradigm has been implemented in several systems [1,2,9,11] and adopted in a wide range of use cases. Here, we present the latest major release, Ontopv4, of a popular VKG system.