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3-tier architecture
This conceptual model shows a three-tier architecture in the form of a web merchant application. The three-tier architecture is a principle of software design that, for reasons of efficiency, separates software processes into layers. In other words it divides the application into areas based on various stages or tasks in a process. The presentation layer, for instance, receives requests from the application layer to present some data and if input is received through a user interface, for example, hands that input down to the application layer (aka business or middle layer). The application layer might process the request from the user interface and send instructions to the database layer to store or retrieve a piece of data (maybe it checks prices or inventory for example). And the database might return the data to application layer for processing and to carry out the entire process again and again.
Posted by Mark Hemphill on February 2, 2004 | Permalink
Comments
Not sure if this question even makes sence.. but whatever.
I'm just going over that 3-tier model in the form of a web merchant application, and i'm a little confused as to why their is two firewalls, one before and after tier 2 (middleware). I always assumed their was one firewall between the internet and the interface.
Having to go through the firewall twice in my opinion is too much protection and will cause problems. I'm not sure if the diagram you have posted is consistent with all web applications. But I do know that if it wasn't for windows XP firewall, i'd be out of a job right now; since more then half the calls we get are no dataflow calls because of xp firewall.
This might be a little off path, sorry.
Posted by: Ricky | Mar 14, 2005 1:10:10 PM
Here is a good site showing different firewalls. Figure 5 shows a three or more tiered firewall topology and Figure 6 is a more complex multi-tiered firewall. Hope this helps.
HERE
Posted by: Robyn | Mar 14, 2005 2:23:16 PM
Here is a good site showing different firewalls. Figure 5 shows a three or more tiered firewall topology and Figure 6 is a more complex multi-tiered firewall. Hope this helps.
HERE
Posted by: Robyn | Mar 14, 2005 2:24:16 PM
Hey Ricky, oh yes most, if not all, web applications would have two layers of firewalls. It's important to contrl access to the application logic (the middle layer) which might be accessible online.....but it's extra important to protect the integrity of the underlying data (i.e where account information might be stored)so a second firewall is needed.
Posted by: Mark | Mar 14, 2005 5:43:25 PM
Yeah I can understand that.. but whats the point when its going to cause dataflow problems all the time?
Posted by: Ricky | Mar 14, 2005 6:23:12 PM
OK, I saw the diagram for the web client/server 3 tier architecture. The only problem I have with the conceptual models, is that I can`t associate something logical with the diagram.
The tier 1 says presentation - is this the end result that shows up on your screen? Tier 2 is middleware, says business logic. Is this the actual application? And tier 3 says the backend, which is the service. What is the service?
It says superbowl ads. Can you explain to me what each tier is doing? Plus, when I click on enlarge the image, it doesn`t enlarge, so I can`t see what the other text says, it could even possibly answer my own questions. Thanks
Posted by: Kim MacKay | Mar 15, 2005 8:12:55 AM
I think Kim is saying the same thing I said a few days ago, and like her, I am not sure if I am seeing it right. Is the Tier 3, the backend, the database? That's how I understood it. Sometimes I think it seems too simple to be on the right track.
I understand Mark's comment on the firewalls, but why does Ricky say the firewalls cause dataflow problems?
Posted by: Anton Mikhailov | Mar 15, 2005 4:07:30 PM
The diagram of the 3-tier architecture really makes it clear to understand what is going on with a webpage. It makes it clearer to see what the 3 tiers are, where they are and what exaclty each tier does. I didn't realize all that went on just to get a webpage to come up.
Posted by: Amanda | Mar 14, 2006 11:44:18 AM
The image is not getting enlarged due to which the text along with the diagram is not visible.
Posted by: abi | Oct 2, 2007 3:12:43 PM
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