RELIABILITY AND

ITS PRINCIPLES

Dr. Himanshu Hora

SRMS College of Engineering & Technology

Bareilly (INDIA)

What is Reliability ?

• Software reliability is defined as the probability of failure free software operation for a specified period of time in a specified environment.

• It is one of the attribute of software quality.

There are four factors associated with Reliability:1) Numerical Value:

The numerical value is the probability that the product will function satisfactorily during a particular time.

2) Intended Function:

Product are designed for particular applications and are expected to be able to perform those applications.

Reliability

3) Life.How long the product is expected to last. Product life is specified as a function of usage, time, or both.

4) Environmental ConditionsIndoorsOutdoorsStorageTransportation

Reliability

Aspects of reliability

• Design

• Production

• Transportation

Design

The most important aspect of reliability is the design.

It should be as simple as possible. The fewer the number of components, the

greater the reliability. Another way of achieving reliability is to have a

backup or redundant component (parallel component).

Reliability can be achieved by overdesign. The use of large factors of safety can increase

the reliability of a product. When an unreliable product can lead to a

fatality or substantial financial loss, a fail-safe type of device should be used.

The maintenance of the system is an important factor in reliability.

Cont…

Production

The second most important aspect of reliability is the production process.

Emphasis should be placed on those components which are least reliable.

Production personnel

Transportation

The third most important aspect of reliability is the transportation. Packaging Shipment

Performance of the product by the customer is the final evaluation.

Good packaging techniques and shipment evaluation are essential.

Reliability Management

Select components, designs, and vendors that meet reliability and cost criteria.

Determine reliability requirements for machines and equipments.

Analyze field reliability for improvement.

Availability and Maintainability

For long-lasting products and services such as refrigerators, electric power lines, and front-line services, the time-related factors of availability, reliability, and maintainability are interrelated.

Availability

It is a time-related factor that measures the ability of a product or service to perform its designated function.

The product or service is available when it is in the operational state, which includes active and standby use.

Avalibility(cont..)

A = MTTF MTTF + MTTR

MTTF= Mean time to failureMTTR=Mean time to repair

Maintainability

Maintainability is the probability that a system or product can be retained in, or one that has failed can be restored to, operating condition in a specified amount of time.

Maintainability is the totality of design factors that allows maintenance to be accomplished easily.

Preventive maintenance reduces the risk of failure.

Corrective maintenance is the response to failures.

Cont…

Principles

Principles of software Engineering: 1) Manage using phased life cycle plan. 2) Perform continous validation. 3) Maintain disciplined product control. 4) Use modern programming practices. 5) Maintain clear accountabilty for results. 6) Use better and fewer people.

Principles of software validation: 1) Requirements 2) Defect Prevention 3) Time and Efforts 4) Software life cycle plans and procedures 5) Software validation after a change 6) Validation coverage 7) Flexibilty and responsibility

Cont…

Thank You

Dr. Himanshu Hora

SRMS College of Engineering & Technology

Bareilly (INDIA)