Saturday, March 7, 2009

System Development Concept (Part I)

The Importance Of Developing An Information System

1. Problems existence
There is a problems from the old system.

2. Organization Growth
Because the requirement is increasing, the system needed to develop.

3. For reach the opportunities
A chance to improve the organization.

4. Instructions existence (directives)
Instruction existence is instructions from the leader or from outside organization, for example regulation of government.

The Purpose Or Goal Of Developing An Information System

1. Solving the problems
2. Reach the opportunities
3. Complete the directives that given

The Organization’s Expectations After Implementing An Information System

1. Performance
In this case, performance is Measured to use and throughput of response time.

2. Information
Increase the quality of information.

3. Economy
Increase the profit and decrease the cost.

4. Control
The Purpose of control is detect and fix the mistakes or error.

5. Efficiency
The organization must to increase the efficiency of operational.

6. Services
Increase the services of system.

The Principles Of Developing An Information System

1. Developed system for the management.
2. Developed system is a big investment
3. The development of system needs educated people.
4. There is a step or process that must be done in system development.
5. System development process must not massage.
6. Don't be afraid to cancel a project.
7. Documentation is important for guidance in system development

System Development Life Cycle Models

1. Waterfall Models

waterfall models

The waterfall model is a sequential development process, in which development is seen as flowing steadily downwards (like a waterfall) through the phases of Conception, Initiation, Analysis, Design (validation), Construction, Testing and maintenance.

In waterfall model, the following phases are followed in order:
1. Requirements specification
The most important task in creating a software product is extracting the requirements or requirements analysis. Customers typically have an abstract idea of what they want as an end result, but not what software should do. Incomplete, ambiguous, or even contradictory requirements are recognized by skilled and experienced software engineers at this point. Frequently demonstrating live code may help reduce the risk that the requirements are incorrect.
Once the general requirements are gleaned from the client, an analysis of the scope of the development should be determined and clearly stated. This is often called a scope document. Certain functionality may be out of scope of the project as a function of cost or as a result of unclear requirements at the start of development. If the development is done externally, this document can be considered a legal document so that if there are ever disputes, any ambiguity of what was promised to the client can be clarified.

2. Design
This Phase is process which focusing at four attributes: data structure, system architecture, interface representation, and algorithm. This phase is translate requirement process into software representation.

3. Construction
4. Integration
5. Testing and debugging
6. Installation
7. Maintenance
This Phase is system maintenance process. System possibly will experience of change after submitted to customer.

1. Ideal for supporting less experienced project teams and project managers, or project teams whose composition fluctuates.
2. The orderly sequence of development steps and strict controls for ensuring the adequacy of documentation and design reviews helps ensure the quality, reliability, and maintainability of the developed software.
3. Progress of system development is measurable.
4. Conserves resources.

1. Inflexible, slow, costly and cumbersome due to significant structure and tight controls.
2. Project progresses forward, with only slight movement backward.
3. Little room for use of iteration, which can reduce manageability if used.
4. Depends upon early identification and specification of requirements, yet users may not be able to clearly define what they need early in the project.
5. Requirements inconsistencies, missing system components, and unexpected development needs are often discovered during design and coding.
6. Problems are often not discovered until system testing.
7. System performance cannot be tested until the system is almost fully coded, and under-capacity may be difficult to correct.
8. Difficult to respond to changes. Changes that occur later in the life cycle are more costly and are thus discouraged.
9. Produces excessive documentation and keeping it updated as the project progresses is time-consuming.
10. Written specifications are often difficult for users to read and thoroughly appreciate.
11. Promotes the gap between users and developers with clear division of responsibility.

2. Iterative Models

iterative models

Iterative and Incremental development is a cyclic software development process developed in response to the weaknesses of the waterfall model. It starts with an initial planning and ends with deployment with the cyclic interaction in between.

There is process or steps of Iterative Model :

1. Initial planning
2. Planning
3. Requirement
4. Analysis and design
5. Implementation
7. Testing
8. Evaluation

The Advantages :
1. Especially useful for resolving unclear objectives; developing and validating user requirements; experimenting with or comparing various design solutions or investigating both performance and the human computer interface.
2. Potential exists for exploiting knowledge gained in an early iteration as later iterations are developed.
3. Helps to easily identify confusing or difficult functions and missing functionality.
4. May generate spesifications for a production application.
5. Encourages innovation and flexible designs.
6. Provides quick implementation of an incomplete, but functional application

3. Spiral Models

spiral models

The spiral model is a software development process combining elements of both design and prototyping-in-stages, in an effort to combine advantages of top-down and bottom-up concepts. Also known as the spiral lifecycle model, it is a systems development method (SDM) used in information technology (IT). This model of development combines the features of the prototyping model and the waterfall model. The spiral model is intended for large, expensive and complicated projects.

The steps in the spiral model can be generalized as follows:

1. The new system requirements are defined in as much detail as possible. This usually involves interviewing a number of users representing all the external or internal users and other aspects of the existing system.
2. A preliminary design is created for the new system.
3. A first prototype of the new system is constructed from the preliminary design. This is usually a scaled-down system, and represents an approximation of the characteristics of the final product.
4. A second prototype is evolved by a fourfold procedure:
  1. evaluating the first prototype in terms of its strengths, weaknesses, and risks
  2. defining the requirements of the second prototype
  3. planning and designing the second prototype
  4. constructing and testing the second prototype
Advantages :
The spiral model promotes quality assurance through prototyping at each stage in systems development.

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