Thanks Farbod.
The Internet today allows individuals and organizations to publish information with very little governance and regulations. It is getting easier and easier to put stuff on an Internet web page. However, not all technical information that is on Internet web pages is accurate. I am not an expert, but I have seen very fancy, nicely done web pages about software development that contains incorrect information. There is no way to prevent this, so the best strategy is to favor published printed material that has been professionally edited and is published by a reputable publishing company, e.g. Addison Wesley, O'Reilly, McGraw Hill
The three-tier model that I describe above is from the Java EE Reference Architecture created by Sun Microsystems(see ref below).
The data access objects (layer) are/is part of the Integration tier. The business objects communicate with the data access objects to send and receive data from the Integration tier.
> So we won't have 4 tier at all? will we?
There is no fourth tier. There is a Presentation, Business, Integration tier.
> Also, if I have a JSP talking directly through JDBC to database, in SQL language, is it still three tier?
No. This design is not in accord with the three-tier programming model from the Java EE Reference Architecture.
> Also what do you answer to the question of advantage and disadvantages of multi-tier over three tier?
See above.
* Sun Certified Enterprise Architecture for
J2EE Technology Study Guide (Sun Microsystems Press) ISBN-10: 0130449164
[ April 22, 2008: Message edited by: James Clark ]