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Two-Tier vs Three-Tier in NFR

 
Marco Bertotti
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Comparing two-tier to three-tier architecture on the NFR part. What's the advantage of two-tier:

availability ? i think it's false because less tier mean less point of failure compare to three tier
manageability (due to each client have a copy of the application) ? i think it's true because less code to maintain
performance (each client have its own objects) ? i think it's false
scalability (due to each client accessing to the database) ? i think it's false due to the fact a DB could have a small pool of connection 

What do you think about those ?
 
Igor Makarov
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Hi. When I was preparing to the exam I understood it in the following way:

In general in N-tier solution scalability, maintainability, availability, performance, extensibility, manageability are better.

But to compare 2-tier and 3-tier need to add additional conditions like clustering in N-tier.

2-tier vs 3-tier non clustered
Advantages:
Availability because less single point of failure.

2-tier vs 3-tier clustered
Advantages:
No real advantages


On the exam make sure that you really understand the details of the questions.

Example:
You have existing 2-tier system and for some reasons you want to make it 3-tier (one web server,one app server, DB). What advantages of existing 2-tier compared to newly created 3-tier.

To answer to the question properly you need to understand whether 3-tier clustered or not. In this example it's not clustered. Therefore [b]Availability[b] is beert in 2-tier.
If it was said that 3-tier clustered then Availability is better in 3-tier solution.
 
Marco Bertotti
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Thanks for the replay.

Both solution are not clustered. So it will be Avalability for sure.
 
K. Tsang
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Given the 4 choices, 2-tier NFR

Availability is a pro because there is less point of failure (namely the server).

Maintainability is a con because of multiple clients. You will need to maintain every client in 2-tier architecture.

Performance in general is a pro because clients use their own computer resources for processing assuming the business logic is in the client side.

Scalability applies to the server side in 2-tier. Adding another server or adding resources to it. Server here can mean just the DB or app + DB, depending where the processing is done.
 
Marco Bertotti
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Due to this Availability is the right answer, also because we have no info on the client hardware and using three tier when client hardware have low resource can led to better performance.
 
Marco Bertotti
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Taking again a look at SCEA book by Cade/Sheil for two-tier it says that advantages are:
- Security
- Performance
and disvantages are:
- Availibility : bacause if one component crashes then the entire system become unavailible.
- Scalability
- Manegability
- Reliability

So should the answer be Performance ??
 
Igor Makarov
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Marco Bertotti wrote:Taking again a look at SCEA book by Cade/Sheil for two-tier it says that advantages are:
- Security
- Performance
and disvantages are:
- Availibility : bacause if one component crashes then the entire system become unavailible.
- Scalability
- Manegability
- Reliability

So should the answer be Performance ??


In that book it's written:
Performance is usually pretty good unless the company uses extremely old laptops that have minimal memory


Performance can't be compared directly in 2-tier and N-tier. Depends on hardware in particular architecture.

Will you have good performance of a video game (with support to play with other palyers over Internet) installed on your PC if you have an old graphic card?
 
Marco Bertotti
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Nope
 
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