Page 197 - Orlicky's Material Requirements Planning

176 PART 2 Concepts

out rigorous file maintenance thanks to the ability of human beings to improvise and to
make up for deficiencies of procedure and file information. Because a machine lacks this
ability, however, rigorous file maintenance is imperative in computer-based systems.

INPUT-DATA INTEGRITY
Because an MRP system entails processing of data on a massive scale, it is virtually
impossible to implement such a system without a computer. A computer, however, func-
tions with full success (unlike a human being) only in a “perfect” environment, which
would include error-free, complete, and timely data. When data lack integrity, any com-
puter system tends to fail. In a system such as MRP, the computer is programmed to
make many decisions (e.g., order size, order release, etc.), and thus because day-to-day
tasks and functions of the business are being performed automatically, system failure
may have far-reaching consequences.
Low-quality input data contribute heavily to such failures and particularly plague
newly developed systems once these go into operation. The quality of input data varies
with their source, and the incidence of errors is always the highest in the data being gen-
erated in factory operations. For purposes of MRP, data are being contributed by plan-
ners, stockroom employees, expediters, dispatchers, inspectors, truckers, and foremen,
all in a position to introduce errors into the system.
Input-data errors cannot be prevented entirely, but it is important that their impact
on the functioning of the system be minimized. It is feasible to incorporate a variety of
external and internal system checks as part of the overall MRP system design, and a qual-
ified programmer can incorporate many auditing, self-checking, and self-correcting fea-
tures into a program. The “war” against input errors should be conducted on three sep-
arate fronts, that is:
1. Erection of a barrier to keep errors from entering the system
2. Programmed capability to detect internally most of the errors that got through
the barrier
3. A procedure for washing out of the system the residue of undetected errors
The barrier, or filter, against input errors may consist of a number of procedures and
techniques. Some form of input audit, testing the formal correctness (Does such a part
number exist? Is this a legitimate transaction code? Are any of the data missing?) is
always desirable. The barrier against the entry of erroneous input is a programmed capa-
bility of the computer system to detect and reject incorrect transactions at the point of
entry, that is, immediately following the input step and before processing begins. Beyond
a formal check at the point of entry, so-called diagnostic routines can be programmed that
will conduct other tests prior to the actual processing of input data. For example, the part
number, transaction code, and so on may be correct, but a diagnostic test against open-
order records indicates that no order has been issued for this item. Diagnostic tests con-
ducted against files other than those to be updated or against special tables set up for this