B. Defining Function and Control Keys : Key Mapping Overview (UNIX and VMS Environments) : Levels of Mapping (UNIX and VMS)
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Levels of Mapping (UNIX and VMS)
The FRS allows you to define key mappings for function, control, and arrow keys on four separate levels:
Terminal type
User (environment)
This allows you to tailor key definitions to the specific requirements of the environment, the terminal type, the user, and the application. The installation‑level mapping has the lowest precedence, and is overridden by all other mappings. Through terminal type‑level mapping, a default can exist for all terminals of a given type, such as VT100s or VT220s. This default is overridden by any conflicting user or application mappings. The user‑level mapping is next in precedence, allowing each individual user a good degree of latitude in the use of function, control, and arrow keys. Application‑specific mappings have the highest precedence to provide the same environment to all users of an application and to ensure data integrity both in the form and the database.
When the FRS starts up, the four levels of mapping are merged and conflicts are resolved based on the precedence outlined previously. Any additional mapping specified by the program during the running of an application is merged in the same manner and takes precedence over conflicting mappings. While the four levels of mappings can coexist, any of the levels can be omitted. Because it is possible that a function, control, or arrow key is defined at more than one of the four levels, the FRS always honors the most recent reference to any mappable key from a file of higher-level precedence.
The following sections discuss each of the various levels at which mapping occurs and how to specify the mapping file for each level.