Software Engineering — SOFTWARE MAINTENANCE [Part-4]

SOFTWARE MAINTENANCE:

Software Maintenance can be defined as the process of modifying a software product after its delivery. The main purpose of software maintenance is to modify and update the software applications after delivery to correct faults(if any) and to optimise performance. Software being a model of the real world needs to be constantly updated to keep up with the real world changes. It is an inclusive activity that includes deletion of obsolete features, error corrections, upgrades and necessary optimizations.

Need for Maintenance:

• Correct faults
• Change in user requirements over time
• Improve the design
• Improving the system efficiency
• Migrate legacy software
• To optimise the code to run faster
• Eliminating any unwanted side effects

Categories of Software Maintenance:

Corrective Maintenance -

This includes all the modifications and updates done in order to rectify bugs and find solutions to specific problems which are either discovered by the user or concluded by user error reports.

Adaptive Maintenance -

It includes all the modifications and updates done to keep the software up-to-date and in tune to the always changing world of technology and business environment.

It implies that adaptive maintenance includes the modifications and updates when the customers need the product to run on new platforms, on new operating systems, or when they need the product to interface with new hardware and software. 

Preventive Maintenance -

 This includes modifications and updations to prevent any future problems with the software. It aims to attend to problems, which are not significant at this moment but may cause serious issues in future. This ensures that the software doesn’t die out.

Perfective Maintenance -

It defines improving the processing efficiency or performance and/or enhancing changeability. This may contain enhancement of existing system functionality, improvement in computational efficiency, etc.  It includes new features, new user requirements for refining the software and improving its overall reliability and performance.

Challenges to Software Maintenance:

• A software maintenance process is an open ended process, continuing for years which drives up the maintenance cost.
• Changes made are often left undocumented causing conflicts in the near future.
• The standard age of any software is in the range of 10-15 years, after which it starts fading, unable to keep up with the world.
• Older softwares originally meant to work on less advanced machines find it hard to compete with new enhanced softwares on modern hardware.

SOFTWARE RELIABILITY:

Software Reliability implies Operational reliability. It is described as the ability of a system or component to perform its required functions under static conditions for a specific period of time.

Software reliability can also be defined as the probability that a software system fulfills its assigned task in a particular environment for a predefined number of input cases, assuming that the hardware and the input are error free. It is an essential component of software engineering and consists of - functionality, usability, capability, serviceability, documentation and installability of the software.

Software reliability is inversely proportional to the complexity of the software. However, that does not deter system developers from pushing a certain complexity level into the software layer. It is believed that the more advanced the technology, the higher complexity of software involved. For instance, the upcoming International Space Station will have an estimated 10 million lines of ground support software; next generation air traffic control systems with about 1-2 million lines of software. To put it in plain terms, we can not sacrifice software complexity for a better reliability since software complexity raises the overall quality of the software.

SOFTWARE FAILURE: 

When the user perceives that the software has ceased delivering the desired result with respect to specific input values, it can be said that software failure has occurred. This can occur for a variety of reasons like - bugs, ambiguities, misinterpretation of the specification that the software is supposed to satisfy, carelessness in writing code, inadequate testing, incorrect or unexpected usage of the software or other unforeseen problems. 

Software failure can be classified as:

• Transient failure: These failures only occur with specific inputs.
• Permanent failure: This failure appears on all inputs.
• Recoverable failure: System can recover without any help from the operator.
• Unrecoverable failure: System can recover with operator help only.
• Non-corruption failure: The failure does not corrupt the system state or data.
• Corrupting failure: It damages the system state or data.

RISK MANAGEMENT:

Risk is a problem that can be a potential threat to the progress of the project in the near future, but hasn’t occurred yet. These potential issues might harm cost, schedule or technical success of the project and the quality of the software device, or cost the project team morale.

Risk Management is the process of identifying, addressing and eliminating these problems before they can cause damage to the project.

Risks affecting a software project can be classified into:

1. Project Risks
2. Technical Risks
3. Business Risks

Project risks: Project risks concern different forms of budgetary, schedule, personnel, resource, and customer-related problems. A vital project risk is schedule slippage. Since the software is intangible, it is very difficult to monitor and control a software project. It is very hard to control something which cannot be identified. 

Technical risks: Technical risks concern potential method, implementation, interfacing, testing, and maintenance issues. It also consists of an ambiguous specification, incomplete specification, changing specification, technical uncertainty, and technical obsoleteness. Most technical risks actually appear due to the development team's insufficient knowledge about the project and/or incompetence.

Business risks: This type of risks are more about the business aspects than the technical aspects. For instance, losing budgetary commitments, building expensive projects with no market demands, etc can be termed as business risks.

Other Risk Categories:

• Known risks - These risks can be identified and subsequently taken care of, after careful assessment of the project program, the business and technical environment and accessing data sources.
• Predictable risks - These risks are hypothesized from past experience of a similar project.
• Unpredictable risks - This type of risks can and often do occur but are tough to identify in advance.

Essential Principles of Risk Management:

Global perspective: 

Reviewing  the bigger system description, design, and implementation. We take a look at the chance and the impact the risk is going to have.

Open communication: 

Encouraging open lines of communication between the client and the team enables certainty and concise plan of action against the risks.

Foresighting:

Contemplating and foreseeing future events help us a lot in forming strategies to deal with future risks and anomalies.

Integrated management:

Risk management is made an essential part of project management.

Continuous process: 

In this phase, the risks are often tracked continuously throughout the risk management paradigm.