This. typically includes the values of? all of the control 
parameters so that non-data-dependent errors can be 
regenerated. Data dependent errars are harder — the image 
data generating the problem may have to be kept available. - 
6. 8. 4 NON-DETECTABLE PROGRAMMER ERRORS. In the case 
non-detectable programmer errors, the application program 
may behave very badly. Nasty program aborts, infinite 
loops, incredibly unreadable operating system error messages 
spew forth on the analyst’s console. These problems are 
meant to be solved as they show up, usually by the 
embarrassed supplier or bu frustrated in-house maintenance 
staff. Fortunately, mature software packages have few of 
this type of error, 
4.8. 5 DETECTABLE OPERATOR ERRORS. These consist of every 
conceivable thing the analyst might mistype at his console. 
The interface must catch as many of them as possible, 
without compromising the application independent nature of 
the interface handler. All error messages at this level 
might be kept in the control parameter dictionary - for 
translatability. These messages must be worded carefully 
and documented throughly. 
6.8.6 NON-DETECTABLE OPERATOR ERRORS. This variety results 
from legal but non-sensical operator set-up. On-line 
documentation should be lucid enough for the 
operator/analyst to understand when he has made such an 
error, and hou to recover from the problem -— usually by 
restarting his procedure. 
5.58 7 MET/S STOR AND START OUER" ERRORS. These are the 
most important ones. If the analyst has kicked off an 
execution run and realizes that he hasn't set it up the way 
he meant to, then there should be some way, via the 
interface handler, to halt the entire process, recover files 
that are in unknoun states, fix his error, and restart. All 
this must be done under the auspices of the interface, and 
without waiting for the error to run to its natural. (or 
unnatural) completion. The solution te this problem 
requires a lot of thought, especially when running nested 
procedures. Usually a special application-dependent 
clean-up program or procedure must be invoked by the 
interface after actual abortion of the application process. 
Asychronous terminal I/0 must be employed: since the 
keyboard cannot be left unguarded while an application 
process is executing under the interface. Some operating 
sustems may not support the necessary cepabilities. 
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