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Sunday, January 29, 2012

What are the different quality attributes in software architecture?

Software is of no use without good quality. Incorporating high quality in software is very difficult. The term “quality” is itself very hard to be defined. We can only measure quality using certain attributes. These attributes are called software quality attributes.

1. Quality attributes of a software system or application define its behavior.
2. The quality attributes give a certain idea of how much suitable is the software for a purpose or environment.
3. It is an essential component of software architecture.
4. Identification of quality attributes is necessary as it helps the system to be built according to the intended behavior.

Certain scenarios are used to measure the quality attributes.
1. The scenarios are very helpful in helping the program developer to make decisions that are qualitative in nature and related to the program behavior.
2. Writing good scenario statements is very important in identification of quality attributes.
3. Although the scenarios help in the identification of attributes, they don’t provide an effective way to achieve those attributes that has to be figured out separately.

Architectural methodologies come to help at this point.
1. There are several architectural methods possible to achieve a particular quality attribute.
2. The software architect should select the right method and use it according to the needs of the software.
3. He should justify the selection of a method and provide documentation on it.

Over the years, some basic quality attributes have been identified and recorded in a list. The quality attributes have been classified in to 4 categories:

1.Run-time system qualities
These attributes are measured when the software is in execution mode.
- Functionality is the ability via which the system completes the assigned task.
- Performance is the collective measure of resource utilization, the response time, and the through put of the system.
- Security is the ability of the system to protect itself from unauthorized access and modifications.
- Availability is the time period for which the system is available to use.
- Inter-operability is the ability of a system to run in cooperation with another system.
- Usability includes other attributes like affect, control, help, and efficiency.

2.Non runtime system quality attributes
These attributes cannot be measured when the software is in execution mode.
- Portability is the ability of a system to perform well in varying environments.
- Modifiability is the adaptive ability of a system by virtue of which it is able to adapt to the changes.
- Integratibility is the ability of the components of the system to work in coordination with each other.
- Reusability is the measure of extent to which the existing features can be used in new software.
- Testability is the measure of the extent to which the software can be tested.

3.Business quality attributes
These attributes affect the other quality attributes.
- Marketability is the value of the system in the market.
- Cost is the money value of the software.
- Schedule is the expected utilization of the system.
- Appropriateness

4.Architecture quality attributes
These are specific attributes concerning the software architecture.
- Correctness is said to account for over all satisfaction of the system requirements.
- Conceptual integrity is the ability of the components of a system to integrate with each other.

5.Domain specific quality attributes
These are specific attributes concerning the business domain.
- Calibrability is the ability of a software system by virtue of which it recalibrates itself according to a specific range of work.
- Sensitivity is the measure of response of the software system to the measuring of a quality attribute.

The software architecture is greatly influenced by the quality attributes of a system. A measure taken in favor of one quality attribute often goes against another.

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