Database Services
Autonomous Database
Autonomous Database is self-driving (automatic tuning, scaling and patching), self-securing (encryption by default, security patches) and self-repairing (automated backups, automatic failover in dedicated deployments). Workloads include Autonomous Transaction Processing (ATP) for OLTP and Autonomous Data Warehouse (ADW) for analytics, plus JSON and APEX options; you pick a workload when provisioning. Two deployment modes: Serverless, where Oracle manages the infrastructure and you scale OCPUs elastically, and Dedicated, where the database runs on Exadata infrastructure dedicated to your tenancy.
Base Database Service
When you need control, Oracle Base Database Service runs Oracle Database on virtual machines, bare metal or Exadata DB systems, with single-node or two-node RAC for high availability, Data Guard for standby replication, and standard editions or Enterprise Edition. Here you patch the guest OS and schedule backups yourself, unlike Autonomous Database. Oracle also offers MySQL HeatWave for MySQL workloads with analytics acceleration, and Oracle NoSQL Database for key-value and document data.
Exam traps
Do not assume a question about "hands-off, DBA-free operations with automatic backups" is asking for a DB system - that is Autonomous Database. Conversely, if the scenario demands OS-level access, custom parameters or specific topology control, the answer is a DB system. Also remember Autonomous Database scales storage automatically and takes backups automatically; you do not configure RMAN.
Rule of thumb
Match the workload, not the feature list: many small OLTP apps and mixed workloads → ATP; reporting and large analytical scans → ADW; full administrative control or existing licensed Oracle Database → Base Database Service.