The layer responsible for altering a database after receiving a request is the database management layer. In standard database architecture, the database management system acts as the software layer that processes requests, enforces rules, and performs operations such as insert, update, and delete. When an application or user submits a query or transaction, the database management layer interprets the request, checks permissions and constraints, manages concurrency so multiple users can work safely, and then applies changes to the stored data. It also helps ensure reliability through transaction controls such as commit and rollback, which protect data integrity when failures occur. The application layer is where the user interface and business logic typically run, but it does not directly manage the physical storage and controlled updates of the database. The flat-file layer is not a standard layer in modern database applications, and object-oriented layer refers to a programming design style rather than the core DBMS component. Therefore, the correct layer is the database management layer.