In the end of thin, the thinnest is the minimal set transferred that
supports the UI and nothing else.
To do this well requires a lot of design, the telnet sessions/terminal
emulators are a classic case of this - only UI information gets transferred
and nothing else.
Technically you can go better than this, but that does not occur with GUI
interfaces as the interface is more rich, so you end up transferring more
data to support the richer GUI.
You can transfer the data either using sockets or CORBA - it depends on your
skills, time frame, required flexibility and money.
You have the same design issues if you use CORBA or Sockets, just don't
expect fast response if you use corba and call a different method to get
each property value on an object - you would be unlikely to do it this way
with sockets anyway. You just have to remember that every call done is
remote across a network. If you are transferring large amounts of data, the
CORBA overhead is not significant (and has been reduced in the latest
GIOP/IIOP spec).
Will Corba work across a 56k modem - YES, you just have an appropriate
object design - In fact it can start to look very much like a optimised
Virtual TDataSet, but only the data required to display the UI is
transferred instead of the complete datasets.
eg Image a listbox with 1000 items, You virtual list box knows it has 1000
items, but only requires to display 20 at time, and you can scroll to any
part and just transfer the data required to be displayed for that position
in the list box. The only data required to be transferred is the description
and a Index/reference for each description to locate the appropriate object
(or whatever) back on the server.
Myles.
> -----Original Message-----
> From: Richard Vowles [SMTP:[EMAIL PROTECTED]]
> Sent: Friday, September 03, 1999 8:05 AM
> To: Multiple recipients of list delphi
> Subject: CORBA (was Re: [DUG]: Thin Database Components.)
>
> Nic Wise wrote:
>
> > Remember, and Annie will hate me for saying this, but Delphi's CORBA
> > stuff is licenced by the SERVER, not by the CLIENT (MIDAS is different,
> > I think?).
>
> Stepping into this conversation without actually reading the thread
> (sorry), the
> answer to that is no - MIDAS is normally licensed per server as well. It
> gets a
> little confusing - if you buy MIDAS then CORBA capability comes as part of
> the
> package, but you can buy just CORBA on its own if you like. MIDAS can be
> licensed
> per client though, and so can CORBA but it just depends - always talk to
> your
> local Annie. I would be very careful to examine the cost/benefit of the
> situation
> - usually MIDAS and/or CORBA work when you have one of two situations:
>
> 1) you have a one off which the customer is paying you for and writing a
> marshalling layer (your own layer on top of sockets to move data) and an
> intelligent data manipulation layer would be too expensive for a small
> job. This
> would normally occur in a custom built package.
>
> 2) A package you are writing where you believe that you will sell volume,
> and
> therefore can get volume discounts. Unless you are selling volume, then it
> is
> usually unlikely that you can get them, but each situation differs so
> asking Annie
> is a good thing.
>
>
> > Get a replacement ORB for Visi - and there are loads out
> > there for free - and your home free - or at whatever cost the ORB ends
> > up being. I haven't tried this - and I dont know of anyone who has - but
> > it SHOULD work, as they all use IIOP as the transport - thats exactly
> > the POINT of CORBA!!!
>
> Although this is true, there aren't any written in Delphi (have some free
> time
> Nic? <grin>). The one used in Delphi is actually Visi for C++ and it has a
> COM
> layer written on top of it. Because of the COM layer, it is heavily tied
> into Visi
> for C++ and thus you are extremely unlikely to be able to place another
> ORB in
> there.
>
> > IMO, I'd go with Visi unless the cost was THE overriding factor -
> > remember, there are always three things wanted - good (ie, low) price,
> > on time, good (ie, high) quality. You can only ever have 2. :)
>
> If you are looking at Java ORBs for the server, then there are a number of
> good
> free ORBs around.
>
> Richard
> --
> Richard Vowles, Senior Systems Engineer,
> Inprise New Zealand
> MAIL: [EMAIL PROTECTED], [EMAIL PROTECTED]
> HTTP: http://www.esperanto.org.nz
> [my messages contain my own opinions, not those of my employer]
>
>
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