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Thursday, 17 December 2015

Two Tier Software Architecture

Two Tier Software Architecture
Two tier architectures consist of three components
1.User System Interface (such as session, text input, dialog, and display management services)
2.Processing Management (such as process development, process enactment, process monitoring, and process resource services)
3.Database Management (such as data and file services)
distributed in two layers:
1.client (requester of services) and
2.server (provider of services).
The two tier design allocates the user system interface exclusively to the client. It places database management on the server and splits the processing management between client and server, creating two layers.
In general, the user system interface client invokes services from the database management server. In many two tier designs, most of the application portion of processing is in the client environment. The database management server usually provides the portion of the processing related to accessing data (often implemented in store procedures). Clients commonly communicate with the server through SQL statements or a call-level interface.
Applications:
1.In non-time critical information processing where management and operations of the system are not complex.
2.In decision support systems where the transaction load is light.
3.In relatively homogeneous environments with processing rules (business rules) that do not change very often and when workgroup size is expected to be fewer than 100 users, such as in small businesses.
Scalability:
The most important limitation of the two-tier architecture is that it is not scalable, because each client requires its own database session. The two tier design will scale-up to service 100 users on a network. It appears that beyond this number of users, the performance capacity is exceeded. This is because the client and server exchange "keep alive" messages continuously, even when no work is being done, thereby saturating the network.
Implementing business logic in stored procedures can limit scalability because as more application logic is moved to the database management server, the need for processing power grows. Each client uses the server to execute some part of its application code, and this will ultimately reduce the number of users that can be accommodated.

Interoperability:

The two tier architecture limits interoperability by using stored procedures to implement complex processing logic (such as managing distributed database integrity) because stored procedures are normally implemented using a commercial database management system's proprietary language. This means that to change or interoperate with more than one type of database management system, applications may need to be rewritten. Moreover, database management system's proprietary languages are generally not as capable as standard programming languages in that they do not provide a robust programming environment with testing and debugging, version control, and library management capabilities.

System administration and configuration:

Two tier architectures can be difficult to administer and maintain because when applications reside on the client, every upgrade must be delivered, installed, and tested on each client. The typical lack of uniformity in the client configurations and lack of control over subsequent configuration changes increase administrative workload.
Batch jobs
The two tiered architecture is not effective running batch programs. The client is typically tied up until the batch job finishes, even if the job executes on the server; thus, the batch job and client users are negatively affected.
Disadvantages:
Performance will be reduced when there are more users.

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