Re: Client/Server Applications - what to use?

["John Taylor" <john.taylor@xxxxxxxxxxxxxxx>]

Ian Clark wrote:

> I have an application to write that I feel would benefit from a graphical,
> ie VB5 front end. My question is - what is the best way to link the
> application to the as/400....APPC, Data Queues, RDO/VDO, ODBC, etc, etc.
> There would need to be a certain amount of validation to be performed on
> various input fields, so constant communication between the two is
> imperative.  Any ideas or pointers would be appreciated.

If you're committed to using VB, or another Win based client, then I'd
recomment that you use ADO/OLE DB. This is MS' (latest) strategic data
access technology, and is therefore the place where you're likely to see the
most development effort.

Using OLE DB, you'll have the option of selecting from SQL access, record
level access, data queues, running OS/400 commands and calling OS/400
programs. You'll probably end up using a combination of those in anything
but the most trivial of applications. For example, I'll use SQL stored
procedures when retrieving multiple rows of data to populate a listbox,
record level access when I need fast access to a small amount of data (ie:
validation), and data queues to notify the PC client when an OS/400 batch
job has completed.

Another option, would be to create your own application servers on the host.
You would communicate with the servers using TCP/IP sockets. There are
definite advantages to doing this, but I wouldn't recommend it if this is
your first foray into client/server. If you're just getting your feet wet
right now, then stick to the middleware products. You'll have enough to
learn as it is.

Whichever technology you decide to use, do yourself a _huge_ favour by
putting all of your data access code into a separate application layer in
order to insulate yourself from the specifics of your database, and the
frequent jumps to the next holy grail of middleware.


Regards,

John Taylor
Canada

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