Server Modules
The main difference between RAMP applications run in VLF-WIN and VLF-ONE is that in VLF-ONE the database IO is done by calling a server program and receiving back the data, whereas in VLF-WIN the database IO is done directly. This difference applies to all database IO, whether in filters, command handlers, pop up prompters etc.
Once you have created the equivalent VLF-ONE components that handle this change, your RAMP application runs largely as it did within VLF-WIN.
In VLF-ONE all database IO has to be done as a call to a separate Server Module.
Data is exchanged between the filter and the server module as fields, groups, or lists.
VLF-ONE is Single Threaded
Another major difference is that VLF-ONE environment is single threaded. This means you cannot display a "please wait" message and then start some synchronous long running operation because the visual message will only get displayed when the operation is finished.
In situations like this you can either:
- Display the message and then start a timer that will initiate the long running operation (See DF_FILTCO for an example).
- Display the message and call the long running operation asynchronously (See DF_T52F1O for an example).
VLF-ONE Applications Work Best With Many Small 5250 Sessions
Another significant difference is the use of 5250 sessions. VLF-WIN and VLF-WEB applications often have a single large and complex navigation tree because in these applications it is not possible to navigate between destinations defined in different 5250 application sessions.
This design issue does not exist in VLF-ONE applications because navigating to different 5250 destination screens is achieved by switching (or invoking) the target business object instead. See 5250 Application Session Guidelines.