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5-2
• Parse the Returned Strings thoroughly. Don’t assume anything
about the next response from the Server to your program and look
only for the partial string such as the ID only. Parse the string
returned completely, and be sure you are examining every
possibility. Failure to do so is a common mistake.
• Plan for expansion. You may start small (1 Terminal) but try to
create an application that will allow for easy expansion.
• Use the Test Program. The test program can at least allow you to
see how the system functions and whether you can anticipate any
system-wide problems. The test program should also be used as a
response-time benchmark.
• Study the Demo Programs. Demo programs are included for
examples of how to use the ActiveX tool provided.
Failure Planning
Hardware Failures
Let’s assume that each part of the system has failed. How are you going to
know what has happened and how are you going to recover?
• The most frequent failures are at the Terminal level. If a Terminal has
a hardware failure, it will not be able to SIGN OUT. It is possible for
the Terminal operator to press the ON/OFF key or the F1 key by
accident, forcing the Terminal to SIGN OUT - sometimes in the
middle of a transaction. This happens at battery-changing time also.
You need to plan for partial transactions - do you trash the data you do
have and start over, or pick up where you left off?
• Keep in mind that if a Terminal has SIGNED OUT in mid-transaction,
the Server clears any pending message for that Terminal before it will
allow it to SIGN ON again. Make allowances to re-send messages or
prompts that were cleared upon SIGN ON if necessary.
Operator Errors
•
Plan on your operator walking out of range and going to lunch in
the middle of a transaction. What do you do with the data you do
have, and where are you going to start up again?
• Let’s say your operator is SIGNED ON and decides it’s time to take a
break. Instead of pressing the F1 key to SIGN OUT, he presses the
OFF key. Pressing the OFF key is OK (it will SIGN him OUT) but
there is a delay until the SIGN OUT is acknowledged. Because of the
delay, the operator might think he didn’t press the key hard enough
and press it again - this time actually powering down the Terminal
before the SIGN OUT was complete. If this happens, you need to plan
to re-send the last prompt to the Terminal when he SIGNs ON again.