On 2/09/99 at 20:16 Tony Blomfield wrote:
> By "Thin" I am referring
>to designing applications in such a way as to minimise the network traffic,
>Take a look at a telnet session into an AS400 as an example of
>"Thin" within this definition.
>I am not a three tier expert, but I find it
>hard to beleive that a three tiered object brokering approach can be an
>efficient model for slow networks
It depends how you're coding things (of course!).
Those telnet sessions are fairly network intensive too. *Every* keystroke is sent
individually across the network, interpretted by the AS400, and an escape sequence
sent back across the network instructing the telnet application to update the screen
to reflect the new-look screen.
Image I have a multi-tier system that handles the processing of an order. The client
tier is some simple HTML form. I click the 'submit button' and information about the
product code and quantity is sent to the middle tier. The middle tier holds my
business logic, and the database. It will need to:
- Checks my security, by hitting a number of database tables
- Checks my credit status, by hitting a number of database tables
- Creates a new order record, by inserting into a database table
- Creates an order detail record, by inserting into a database table
- Produces a picking-slip, by printing a bit of paper on a printer connected to the
server
- Updates sales analysis tables
- Lots more stuff, but you're getting the idea by now.
The only stuff that's gone across the network has been the product, quantity, and
(maybe) customer information. All that network traffic related to SQL calls has all
occured on the server. In a 2-tier setup, the SQL statements would all have had to be
sent up to the server (over the network) and the results sent back down to the client
(ditto).
The other beauty of an n-tier architecture is the reduction in required resources,
like database connections. In a 2 tier setup each client tends to need its own
connection. In an n-tier environment they're more likely to be shared, so the server
needs less memory, and you probably need to buy less database licenses.
I'm sold on the idea.
Cheers,
Kerry S
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