2-tier architecture ?

[Piotr Uryga]

Hello Ranchers !

I'm a little bit confused by whizlabs SCEA simulator.
In one of questions we have architecture which consists of:
- 3 clustered web servers
- db with business logic implemented in PL/SQL

In the other we have:
- Apache web server for presentation and business logic
- separate server for the Sybase db

Both questions among the good answer choices have "thin clients".
So far, so good...
but they are also described as 2-tier architecture.
Am I crazy or these are simple samples of 3-tier architecture (thin client, middleware and DB) ?

Thanks in advance for Your answers.
Piotr

[Dan Drillich]

Hi Piotr,

http://www.orbeon.com/blog/2005/02/17/3-tier-architecture-versus-service-oriented-architecture/

It says:

For instance, on the Java platform, the presentation layer could be implemented with JSP and JSF, the business layer with session EJB, and the data layer with entity EJB or Hibernate.

In the whizlabs SCEA simulator examples:

- 3 clustered web servers
- db with business logic implemented in PL/SQL

The 3 clustered web servers is a physical layer and the two application layers are the thin client and the logic implemented in PL/SQL.

- Apache web server for presentation and business logic
- separate server for the Sybase db

Separate server for the Sybase db is a physical layer and the two application layers are the thin client and presentation and business logic bundled together.

Regards,
Dan

[Newman Huang]

i think this is a simple&complicated question. in traditional fat client application, the client fetches data from server and computes the result. the presentation and business is mixed together in the client side, and the computing consumes the resources of client machine. fad mode is a bad thing such as hard to maintain code, bottleneck happens when a big amount clients connect to server...to avoid these things, 3-tiers came out. the obvious things for 3-tier are diff kinds of 'server' emerge in our sight, web server, app server, also including the old db server. there is no additional client app installed in client machine except for a browser. and so, we can say your client is 'thin' once your application holds a web server. but, i don't think the implementation is undoubtedly real-thin when a web server is used, such as writing java code to implement all the business logic in jsp without obey the MVC mode(at least the MVC1.5 style). okey, go back to the question,

---------------
In one of questions we have architecture which consists of:
- 3 clustered web servers
- db with business logic implemented in PL/SQL

---------------
: sure it is a very very thin client type. the business logic is implemented in the data layer.

---------------
In the other we have:
- Apache web server for presentation and business logic
- separate server for the Sybase db
---------------
: i am not sure because i don't know how it implements the business logic, maybe it uses cgi with perl? if a good separation between presentation and business logic, it is sure a real-thin client, the presentation 'thin' client to the business logic layer(middle server), and the pure business logic 'thin' client to the data server.


any comments?

[Newman Huang]

another point, 2-tier architecture is not equals to 'fat client'.