Characteristics of the Software

Software is a logical rather than a physical system element therefore software has characteristic that

are different then hardware component.

1. Software is developed or engineered; it is not manufacture in the classical sense.

• In both activities software development and hardware manufacturing, high quality is achieved

through good design, but the manufacturing phase for hardware can introduce quality

problems that are nonexistence (or easily corrected) for software.

• Both activities depend on people, but the relationship between people applied and work

accomplished is entirely different. Both activities require the construction of a product, but the

approaches are different.

2. Software does not wear out failure.

• Figure (A) depicts failure rate as a function of time for hardware. The relationship often called

the “bathtub curve” indicates that hardware exhibits relatively high failure rate early in its life.

(This failures are often attributable to design or manufacturing defects);

• Defects are corrected and the failure rate drops to a steady state level (hopefully quite low)

for some period of time.

• As time passes, however, the failure rate rises again as hardware components suffer from the

cumulative effects of dust, vibrations, abuse, temperature extremes, etc. Stated simply,

hardware begins to wear out.

• Software is not susceptible to the environmental maladies that cause hardware to wear out.

• As shown in figure (B), the failure rate curve for software shows that, undiscovered defects

will cause high failure rates early in the life of a program.

• These are corrected (without introducing other errors) and the curve flattens as shown in

figure (B).

• Software doesn’t wear out, but it does deteriorate(go down). During the software life, it will

undergo change (maintenance).

• As changes are made, it is likely that some new defects will introduced, causing the failure

rate cure to spike. Before the curve can return to the original steady-state failure rate,

another change is requested, causing the curve to spike again. Slowly, the minimum failure

rate level begins to rise the software is deteriorating due to change.

• Hardware component wears out; it is replaced by a spare part. There are no software spare

parts.

• Every software failure indicates an error in design or in the process through which design

was translated into machine executable code.

• Therefore, software maintenance involves considerably more complexity than hardware

maintenance.

3. Most software is custom built rather than being assembled from existing components.

 Reusability is an important characteristic of high quality software component.

•  A software component should be designed and implemented so that it can be reused in many different programs.
•  Modern reusable components encapsulate both data and the processing that is applied to the data, enabling the software engineer to create new applications from reusable parts.
• For e.g. today’s interactive interfaces are built using reusable components that enable the creation of graphics windows, pull down menus and a wide variety of interaction mechanisms.
• Software components are built using a programming language that has a limited vocabulary. An explicitly defined grammar and well-formed rules of syntax and semantics.
• At the lowest level, the language mirrors the instruction set of the hardware.
• But Sometimes reusable components does not fulfill the requirement there may be some changes we want but because of its complexity of code means we have to understand the whole component for making some changes to it , which is very complex task instead of this we can create a custom component.