Ask the MultiValued Visual
Basic Expert - #8
(as published in Spectrum
magazine)
To email your questions to "Ask the MultiValued VB
Expert", click here.
Copyright © 1996-97 Caduceus Consulting. All rights reserved.
Laptops and AP/DOS
I often read
your articles in Spectrum magazine and have some questions
regarding a development issue. I have created a order processing
application for laptops, written on AP/DOS. Merchants take their
laptops in the field, enter orders, and perform various analyses
based on downloaded data. That's all great, however, I would like
to interface some Visual Basic programs with this AP/DOS database
and have merchants run the VB programs. The host is the laptop.
My questions are as follows:
- There are
many laptops – are VB run-time licenses required to
execute a VB program?
- Can a VB
program work with AP/DOS or do I need to upgrade AP/DOS?
Is that a costly upgrade for each laptop?
- Is D3 the
only way to upgrade a PICK application running from
windows? Currently they are using Windows 3.1. Do I have
to upgrade them to Windows 95 in order to use any VB
interface?
I know that's
a lot of questions, but if you can help me, I would surely
appreciate it. Thanks. - M. Margulis, New York
Thanks for your
questions – I'm always happy to help out developers like
yourself in any way that I can, so let's see what I can tell you:
Are
VB run-time licenses required to execute a VB program?
Nope. You just
need one copy of the Visual Basic software to develop and compile
the EXE file that you can give to anyone as many times as you
like. VB executables DO require a one-time installation of some
VB functionality files, but these are freely distributable as
well, and VB comes with a setup wizard that can take care of all
of that for you.
Can a
VB program work with AP/DOS or do I need to upgrade AP/DOS? Is
that a costly upgrade for each laptop?
To my knowledge,
VB cannot access AP/DOS files directly without some extra
'middleware'. The only two middleware products that I know of
that can connect VB to AP/DOS are CuebicX from Cuebic Systems
(using objects), and WinLink from Via Systems (using direct
access, objects, or ODBC). You say that the laptop is the host,
but you imply that data is still downloaded from another central
source. Let's look at two scenarios:
If each laptop
has a copy of AP/DOS then it might get a bit expensive for each
laptop to get a full-blown server copy of the required
middleware. If the laptops can be upgraded to Windows 95, you
might consider getting a copy of D3 for Windows 95 for each
laptop. That might be even more expensive than the middleware,
but it would be a more elegant solution under those
circumstances. Visual Basic can access data from D3 directly. I
don't favor this solution because each laptop would be running as
a fully independent host with a separate copy of all of the
required data.
If the laptops
can dial in to a central AP (or other MultiValue flavor) system
(either directly or through the internet), then I would recommend
that scenario. That way, the data is always current, and no big
data download or expensive software is required. Each laptop
would simply require a copy of your VB program and a single
workstation license for the required middleware (which would be
vastly cheaper). The future is heading back to centralized
databases, where we were 15 years ago. If you didn't want to
connect up every time, you could use ODBC or some other similar
transport to grab selected data from the central host and store
it on the laptops for future use.
Is D3
the only way to upgrade a PICK application running from windows?
Currently they are using Windows 3.1. Do I have to upgrade them
to Windows 95 in order to use any VB interface?
Is D3 the only
way? No, it's not (unless you ask Pick Systems, of course!).
There are many terminal emulators that will allow you to make
your existing screens look like they have a graphical
Windows interface. As for a full MultiValue system, running under
Windows, early players in this market were jBASE (from JAC), and
uniVerse NT from VMark. D3 runs under Windows 95 or NT. I believe
UniData also put out an NT version of their flavor, but I have
never worked with it, and now that they are teamed up with VMark,
I don't know what will be happening with that. General Automation
created a new NT-based MultiValue environment called mvŸ BASE, and finally the
UniVision flavor from EDP was also just recently announced as
available under NT. Each NT-based MultiValue database takes a
different (sometimes radically different) approach to their
particular implementation methodology.
I presume that
you do have a central host, although you don't say what
MultiValue flavor it is. Fortunately, if you are connecting the
laptop to a remote MultiValue host, then middleware like CuebicX
and WinLink will talk to just about any flavor, from the old
Sanyo Icons and PI/Open boxes right up to the latest D3 and
uniVerse NT boxes.
Whether you have
to upgrade the laptops to Windows 95 or not depends on the
version of VB that you use. Applications written with VB4
(16-bit) can run under Windows 3.1, 3.11, 95, or NT. VB5
applications will ONLY run under Windows 95 or NT. My advice for
you? If you can find a copy of VB4 (Professional edition), buy
it. In my opinion, while the code editor in VB5 is a little more
helpful, the improved functional capabilities are not that
noticeable for a beginning VB developer, and with VB5 you
lose the O/S choice that 16-bit VB4 continues to offer you.
Furthermore, you can always go from 4 to 5, but you can't go
back! (Of course, the value of this advise will diminish with
time as 16-bit systems continue to fade from the market.)
To email your questions to "Ask the MultiValued VB
Expert", click here.
Copyright © 1998 Caduceus Consulting. All rights reserved.
Compiled: May 6, 1998.
Return to Caduceus
Consulting Home Page
