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.
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.
Regards,
Rob
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