NTier Architecture

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N-Tier Architecture

• Group 7

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Definitions

• Tier
• mean a physical tier defined by a physical
  server, or a group of physical servers that
  perform the same function as each other but exist
  to extend capacity
• Layer
• mean a section of the system that is contained
  within its own process or deployment unit.
  Multiple layers may co exist on one tier, but can
  easily be moved to another tier if some sort of
  remoting capabilities are used.
• Database
• Database are designed to store, retrieve, and
  update data as quickly and efficiently as
  possible.
• Business Logic
• A workflow or procedure that defines the way a
  company conducts business .

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Different Types Of Architecture

• Client Application (One Tier)
• Client/Server (2-Tier)
• 3-Tier
• N-Tier

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Client Application (One Tier)

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Client/Server (2-Tier)

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Client/Server History

• Mainframe Architecture
• File Sharing Architecture
• Client/Server Architecture
• Typically, The Server contain a DBMS
• The Client Take Care of Presentation

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Types Of Client/Server
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Problem Of Client/Server

• The biggest and the most pressing problem at that
  time was one of connection count
• Servers were often licensed per client connection
  
• In the 1990's most databases began to become
  heavily and the speed of database reduced

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3-Tier Architecture

• Come To Solve Client/Server Problems
• A middle layer can solve these problems
  (Transaction processing monitors, Message
  servers, Application servers, Object Request
  Brokers (ORB))

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N-Tier Architecture

• N-Tier An unlimited number of tiers.
• Each tier may have multiple computers.
• Advantages
• More powerful applications
• Many services to many clients
• Enhanced security, scalability and availability
• Disadvantages
• Much more complicated to design and model
• Performance risks
• Reliability is more difficult to achieve
• More difficult to maintain software

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Major Quality AttributesEffects of N-Tier
architectures

• Performance
• Reliability
• Usability
• Security
• Availability
• Scalability
• Maintainability

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Types Of N-Tier Architecture
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Comparison of Architectures
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N-Tier Scenario 1

• The business layer contains no business rules
• The business layer is a database connection
  pooling

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N-Tier Scenario 2

• Typically some of the rules from the application
  are moved to the business layer
• Reused Business Layer

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N-Tier Scenario 3

• All the business logic exists in a single
  location and can be easily verified, debugged,
  and modified.
• A true development language can be used to
  implement business rules. Such a language is both
  more flexible and more suited to such business
  rules rather than the SQL and stored procedures.
• The database becomes a storage layer and can
  focus on efficiently retrieving and storing data
  without any constraints related to business logic
  implementations or the presentation layer.

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Business Layer Advantages

• Increase Number Of Business Layer is Cheaper
• While increasing database server capacity the
  costs are significant for two reasons
• Database server hardware is typically of a higher
  caliber than the middle tier servers and is more
  expensive.
• Databases are very often licensed per CPU and
  adding additional CPU's or servers is costly in
  terms of license fees. License fees can range
  from 5,000 per CPU to 40,000 per CPU.
• Increase Number Of Business Layer is Easier
• Once a load distributor is installed, it's simply
  a matter of adding a new server to expand the
  capacity.
• Need just to install application server rather
  than operation system.

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Topology
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Topology
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Grow the middle Tier

• If significant portions of the business logic are
  implemented in the database, you will need a
  bigger database. The scenario is as follows

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Grow the middle Tier

• By moving the logic to the middle tier, you can
  drastically reduce the load on the database.

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References

• http//www.webopedia.com/quick_ref/app.arch.asp
• http//en.wikipedia.org/wiki/Multitier_architectur
  e
• http//www.codeproject.com/KB/architecture/DudeWhe
  resMyBusinessLogic.aspx
• http//www.15seconds.com/issue/011023.htm
• http//rangiroa.essi.fr/cours/car/ntier.pdf
• http//www.cs.vu.nl/se/slides/5b-ntier-softeng-02
  03.pdf
• http//www.fas.harvard.edu/cscie259/distribution/
  lectures/7/lecture7.pdf