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On-line vs. Off-line
PDTs can access and update host databases in real-time
using Radio Frequency Data Communication (RFDC) or
off-line by batch processing at the end of data collection.
In most cases, batch processing is chosen over RFDC
mainly because of the cost differential. Historically,
this has been the case, however, new technology and
open connectivity solutions now exist to where RFDC
can easily be implemented with most host computers.
When deciding between an RF and batch system, cost
should not only be the deciding factor. Both systems
do have their own benefits and will improve inventory
accuracies.
At a closer look, the risk of losing data is greater
with off-line systems than with RFDC systems. With
most off-line systems, users generally transfer data
once or twice a day mainly for two reasons (1) to avoid
the inefficiency of frequent trips to the batch station
used to upload and download data and (2) to save off
the collected data in the event of a hardware failure.
If a hardware failure were to occur with the PDT, all
the data stored would be lost.
If the end goal is to customize the PDT program
such as simulating access to the host database, programming
cost can be higher for off-line systems, simply because
many computer departments donÕt have developers that
can program in languages such as C, BASIC, or PASCAL.
Most batch PDTs have Resident Operating Programs (ROP)
that are built-in to the reader and allow the users
to easily define the data fields, the number of fields,
the width of each field, prompting messages, and record
delimiters of a file. The ROP is ordinarily flexible
enough to support most data collection applications.
This is generally the reason why most companies purchase
these batch units besides cost and development cycles.
RFDC access to a host database can substantially
reduce unexpected stock outages. Since the data is
centrally stored and accessed in real-time, an accurate
count of the inventory level can be determined instantly.
In addition, discrepancies can be reported immediately
by providing Òat the pointÓ data entry and on-line
validation. When using off-line systems, the benefits
of real-time data entry and on-line validation can
be simulated, but this is usually not practical since
a good part of the time would be spent walking back-and-forth
to record information in pseudo Òreal-timeÓ.
RF terminals have drastically come down in price.
Some manufacturers even allow users to upgrade PDTs
to radio frequency PDTs simply by adding (attaching)
a modular RF transmitter to the terminal. Traditionally,
RF terminals have been designed to emulate common terminal
protocols, and thus a host modification is required
to program RF applications. Some manufacturers allow
access to host computers using development packages
such as MicrosoftÕs Visual Basic or Visual C/C++. Not
only is the development cycle shortened when using
Visual Basic for new applications, but the benefits
of implementing RFDC systems is considerably less in
price since proprietary hardware is no longer required
and access is through a common PC. Application software
can even be purchased to provide connectivity from
the host to the RF terminal.
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