Work Processes

Work processes execute the individual dialog steps in R/3 applications. The next two sections describe firstly the structure of a work process, and secondly the different types of work process in the R/3 System. Structure of a Work Process Work processes execute the dialog steps of application programs. They are components of an application server. The following diagram shows the components of a work process:
Each work process contains two software processors and a database interface.

Screen Processor

In R/3 application programming, there is a difference between user interaction and processing logic. From a programming point of view, user interaction is controlled by screens. As well as the actual input mask, a screen also consists of flow logic. The screen flow logic controls a large part of the user interaction. The R/3 Basis system contains a special language for programming screen flow logic. The screen processor executes the screen flow logic. Via the dispatcher, it takes over the responsibility for communication between the work process and the SAPgui, calls modules in the flow logic, and ensures that the field contents are transferred from the screen to the flow logic.

ABAP Processor

The actual processing logic of an application program is written in ABAP - SAP’s own programing language. The ABAP processor executes the processing logic of the application program, and communicates with the database interface. The screen processor tells the ABAP processor which module of the screen flow logic should be processed next. The following screen illustrates the interaction between the screen and the ABAP processors when an application program is running.

Database Interface

The database interface provides the following services:

• Establishing and terminating connections between the work process and the database.
• Access to database tables
• Access to R/3 Repository objects (ABAP programs, screens and so on)
• Access to catalog information (ABAP Dictionary)
• Controlling transactions (commit and rollback handling)
• Table buffer administration on the application server.

The following diagram shows the individual components of the database interface:



 

Types of Work Process

Although all work processes contain the components described above, they can still be divided into different types. The type of a work process determines the kind of task for which it is responsible in the application server. It does not specify a particular set of technical attributes. The individual tasks are distributed to the work processes by the dispatcher.
Before you start your R/3 System, you determine how many work processes it will have, and what their types will be. The dispatcher starts the work processes and only assigns them tasks that correspond to their type. This means that you can distribute work process types to optimize the use of the resources on your application servers.
The following diagram shows again the structure of an application server, but this time, includes the various possible work process types:




The various work processes are described briefly below. Other parts of this documentation describe the individual components of the application server and the R/3 System in more detail.  

Dialog Work Process: Dialog work processes deal with requests from an active user to execute dialog steps.  

Update Work Process: Update work processes execute database update requests. Update requests are part of an SAP LUW that bundle the database operations resulting from the dialog in a database LUW for processing in the background.  
Background Work Process: Background work processes process programs that can be executed without user interaction (background jobs).
Enqueue Work Process: The enqueue work process administers a lock table in the shared memory area. The lock table contains the logical database locks for the R/3 System and is an important part of the SAP LUW concept. In an R/3 System, you may only have one lock table. You may therefore also only have one application server with enqueue work processes. 
Spool Work Process: The spool work process passes sequential datasets to a printer or to optical archiving. Each application server may contain only one spool work process.