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For instance, imagine a small order processing system that could be visualized like this:
| Panel |
|---|
ORDWRK |
| No Format |
| ORDWRK
|
------|------- | | | ORD001 ORD002 ORD003 |
...
--- |
When a user enters this system and begins jumping from ORD001 to ORD002 to ORD003, and so on, a fair amount of computer resource can be wasted opening and closing files used by all the functions.
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To fix this problem we might code a "file opener" called ORD004 that looked like this: OPEN FILE
OPEN FILE(TABLES)
...
USE_OPTION(*KEEPOPEN)
...
OPEN FILE(ORDHDR)
...
USE_OPTION(*KEEPOPEN)
...
OPEN FILE(ORDLIN)
...
USE_OPTION(*KEEPOPEN)
...
CALL PROCESS(ORDWRK)
which would fit into the existing system like this:
| Panel |
|---|
ORD004 |
| No Format |
| ORD004
|
|
ORDWRK
|
------|-------- | | | ORD001 ORD002 ORD003-- |
In this situation, the implicit OPEN and CLOSE requests issued by ORD001, ORD002 and ORD003 are ignored, which results in much faster processing.