Designing Dialogs › Dialog Characteristics › Dialog Level

Dialog Level

The level of a dialog refers to its position within the application structure. You can pass processing control to a dialog at the next lower level, the same level, the next higher level, or the top level of the application structure.

Note: The meaning of TOP changes whenever a LINK command is executed. The dialog issuing LINK becomes the current TOP.

Impact of the Dialog Level

At runtime, the dialog level affects the following aspects of an application:

• Availability of data — When combined with the manner in which processing control is received, the level of a dialog governs the data passed in the record buffer blocks and the currencies that are established, saved, stored, or released.
• Use of system resources — The runtime system maintains record buffer blocks, database currency blocks, and variable dialog blocks for dialogs at each level. There is a direct correlation between the number of dialog levels in an application and the size of the storage pool that is needed.
• Performance — The number of dialog levels can affect the performance of an application. For example, performance times are affected if a frequently accessed dialog is located three or four levels down in an application structure.

An application can be composed of any number of dialog levels, but the most efficient application uses many levels only when absolutely necessary.

Mainline Dialog

The top-level dialog must be a mainline dialog and must be defined as such by the application developer. A mainline dialog is the entry point to the application. An application can have more than one mainline dialog; entry points can also be established at a lower level in the application structure. In addition to defining a task code for the top-level dialog, the developer can identify an alternative entry point by using the Task Codes screen to associate a task code with a lower-level function.