- The application tier (sometimes called the middle tier) consists of a number of servers or services that define the set of processes that will be started on each application node, and can be activated or deactivated according to the function the node is to perform. These include Forms services, Web services, and Batch Processing services (Concurrent Processing server). A key role of these services is to provide communication between the desktop tier and the database tier.
- The database tier consists of the database server, which stores all the data of the Release 12 system in an Oracle database.
A server or service is the term for a process that provides a particular functionality.
A node is a logical grouping of servers and therefore fundamentally a software concept rather than a hardware concept.
A tier is a logical grouping of servers or services, potentially spread across more than one physical machine.