> Filippos Slavik wrote:
> --- Filippos Slavik <[EMAIL PROTECTED]> wrote:
> > > another HTML-SERVLETS-JDBC-ODBC-DBMS as another.
> > None of the above approach belongs to the three tier architecture. In
> > both cases you have a client (java client or java servlet [ about the
> > seconds approach, the servlet, it can be somehow considered as a
> > three tier approach, but this is another story : ])
>
> I think this is an overly strict definition of "three tier". In
particular, I
> have trouble characterizing a servlet as a client. The HTML browser is a
razor
> thin client with absolutely no business logic at all (though you could
throw
> some in with JavaScript) and only presentation via a presentation facade
in the
> application layer. The servlet makes a great location for business logic
and
> allows for a data layer. You really don't have to use "three tier
middleware"
> to get a three tier system. Heck, you can implement a three tier system
using
> only sockets.
>
"The servlet makes a great location for business logic and allows for a
data layer".. this is exactly my point. All about multitiered systems is
(ok there are also other issues involving) that they allow you to partion
your distibuted application into certain modules. Especially when the
discussion comes to "clients" it's very wise to seperate the business logic
with the presentation layer (and there are many reasons to do that).
Personally I don't like the idea to have a servlet doing both .. computing
stuff and then presenting the results. Instead of it, I have used servlets
as a "presentation layer" only and let all the computing to take place in
middleware objects ... which is a very efficient approach. Anyway,
personally, I don't think that "only servlet" approach gives you a real
"thin client"
About the socket stuff... hmm.. Ok, you can get performance speed up, by
using plain socket coding ... but this is the only thing you get among with
hundred of other problems. I think that today building a real-world
multitiered distributed application on plain socket whould be fatal
mistake. CORBA makes things easy but with a certain price to pay.. and
that's performace and bandwidth usage.
> As an added point, it's unwise to assume that a tier maps to a single
process
> on a single machine. In practice, I've seen pieces of the data layer
> implemented in the application layer and bits of "business logic"
implemented
> in the UI (e.g. minimal validation before going over a high latency, low
> bandwidth WAN). When the UI is running a scripting language, it is
trivial (and
> not a violation of the principles of a three tier system) for the
application
> layer to download bits of its logic with the presentation. A good
application
> layer implementation will not rely on the validation, but only use it for
> optimization.
>
I agree with you. Implementing bits of "business logic" into the UI of a
thin client, like data validations, make sence.
> Regards,
>
> Rob
>
Regards
Slavikos
################################################################
Filippos Slavik
Part of the SIAMS's implementation development team. For more
information, please check http://www.siams.net
e-mail : [EMAIL PROTECTED]
################################################################
"The software said 'runs on Win95 or better,' so I installed
it on Linux..."
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