• Presentation Layer
• Business Logic Layer
• Data Access Layer

In most of the cases the data entered by the end user needs some kind of validation or further processing. This is the responsibility of Business Logic Layer.

Finally, your application data needs to be stored and retrieved in some data store (RDBMS, XML etc.). This task is handled by Data Access Layer.

In short, the process works like this:

• User requests for some application data.
• The data access layer retrieves the data and is forwarded to the presentation layer via business logic layer. Sometimes data access layer gives this data directly to presentation layer.
• Presentation layer receives the data to be displayed via business logic layer.
• The user changes the data and initiates the appropriate action (such as insert, or update).
• The business logic layer validates the data submitted by the user.
• If the data is valid it is handed over to data access layer for updating into the database.

• The applications gets divided in logically isolated pieces reducing tight coupling between the UI, business processes and database.
• Change in the underlying database and data access methods do not have any effect on the presentation layer or client application.
• Client application no longer has SQL statements embedded in it. This makes it de-coupled from rest of the application.
• Table and column names can be effectively eliminated from the client-side code.
• The client application is unaware from where data comes (location transparency).
• It becomes easier to modify or extend your application, without breaking or recompiling the client-side code.

TRAPS:  Give a perfect "10," and you'll seem too easy to please.  Give anything less than a perfect 10, and he could press you as to where you're being critical, and that road leads downhill for you.

BEST ANSWER:  Once again, never be negative.  The interviewer will only resent criticism coming from you.  This is the time to show your positivism.

However, don't give a numerical rating. Simply praise whatever interview style he's been using.

If he's been tough, say "You have been thorough and tough-minded, the very qualities needed to conduct a good interview."

If he's been methodical, say, "You have been very methodical and analytical, and I'm sure that approach results in excellent hires for your firm."

In other words, pay him a sincere compliment that he can believe because it's anchored in the behavior you've just seen.