Architecture

The three-tiered architecture divides the architecture into three layers:

* The user interface layer

* The business logic layer ("application" layer)

* The database layer
The 3 tier solution is more scalable.

Now upgrading application is easier as well. The application now resides one (or few) machine: middle tier, as oppose to hundreds of client PCs.

SAP engineers also abstracted the database layer. Many different databases are supported.

The client/server architecture was a two tier solution. The two tiers were: the Server computer and the Client PCs.

Later on SAP engineers constructed a solution that involved three tiers rather than two

A central computer hosts the database.

This computer is known as the database server.

The application server is responsible for the administrative functions including background processing and printing.

Multiple application servers can exist in an SAP three-tiered design.

This is not true for the database server, however.

There can be various computers fulfilling the role of presentation server.

These computers are also called front-end clients.

These computers display the SAP screens.

SAP graphical user interface (GUI), or SAP GUI is installed on these computers.

The four-tiered system enables simple browser-based access.

This laywer helps in reducing the expense associated with installing, patching, and upgrading the SAP GUI user interface across perhaps hundreds or thousands of desktops.

Also it helps to integrate web services into the overall architecture.

Four-tiered architectures

SAP introduced Four-tiered architectures when enterprise software vendors recognized the value that the Internet or company-internal intranets can provide to the end-users.

The fourth layer is called "accessibility tier" or "services tier".

This layer exists in between the application and presentation tiers.