Re: multi-tier architecture

In article <01be6805$55b987a0$2b034f0c_at_blkshear>, JBlackshear_at_worldnet.att.net says...
> We are beginning (or preparing to begin) a project moving our software to a
> three-tier architecture. The main reason is that we need to support
> multiple databases (the application is currently written in Oracle). We
> know we're going to use Java for the middle layer and we're probably going
> to use COM. I don't know much about it - I'm just beginning to read up on
> the subject. Because we're supporting multiple databases, we do not want
> to use a database-specific product like Oracle Application Server.
>
> I have several questions/requests:
>
> 1. Can anyone recommend some good books or articles on design
> considerations for this type of architecture?

3-Tier Client/Server At Work
by Jeri Edwards
The Essensial Client/Server Survival Guide by Robert Orfali/Dan Harkey/Jeri Edwards

These should get you started.
>
> 2. Can anyone recommend some good third-party components for security,
> connection, load-balancing, etc?

I like BEAs suite of middleware products. Take a look at www.beasys.com There are others that migth do a good job as well. If you want to be vendor independent and use Java for the middle tier, it is probably a good idea to check out Enterprise Java Beans.

>
> 3. Does anyone have any advice, rules-of-thumb, etc. for which application
> logic we should move into the application server layer and which we can
> leave in the database? I'm thinking that basic "database rules" (as
> opposed to business rules) would remain in the database: maintaining
> denormalized fields, complex constraints, that sort of thing. Although
> I'll have to simplify my multiple-trigger row-level triggers in Oracle to
> the statement-level-only-one-per-type triggers in Sybase and SQL-Server.
> (I'm not looking forward to that - I love my Oracle triggers.)

Since you want to be database indpendent, it pretty much gives that you have to move most of your business logic to the middle-tier. This is probably a good idea anyway, since it is then easier to change the client too (Java, Windows, html/xml....).

>
> 4. How does executing Java components from triggers compare to triggers
> calling database packages/procedures in terms of speed, memory-use, etc?
>
> 5. How does sending multiple instructions to the database from Java
> compare to sending only a single instruction to the database and letting
> the db handle all of the remaining processing?
>
> Obviously, we're struggling with the eternal flexibility vs. speed
> tradeoff.

Something like BEAs Weblogic application server should be able to give you both. It even runs on the AS/400.

Best of luck,
Haakon
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