The explanation is that a Virtual Cloud Network (VCN) is a software-defined network that you set up in OCI to connect your cloud resources, such as compute instances and databases. A VCN provides you with complete control over your network environment, including selecting your own IP address range, creating subnets, route tables, gateways, security lists, etc. You need to create a VCN before provisioning an OCI DB System, as you need to specify which subnet in your VCN you want to launch your DB System in.