Software is a program or set of programs containing instructions which provide desired functionality . And Engineering is the processes of designing and building something that serves a particular purpose and find a cost effective solution to problems. 

Software Engineering is a systematic approach to the design, development, operation, and maintenance of a software system.

Dual Role of Software: 

1. As a product – 
 

• It delivers the computing potential across network of Hardware.
• It enables the Hardware to deliver the expected functionality.
• It acts as information transformer because it produces, manages, acquires, modifies, displays, or transmits information.

2. As a vehicle for delivering a product – 
 

• It provides system functionality (e.g., payroll system)
• It controls other software (e.g., an operating system)
• It helps build other software (e.g., software tools)

Objectives of Software Engineering: 
 

1. Maintainability – 
   It should be feasible for the software to evolve to meet changing requirements.
2. Efficiency – 
   The software should not make wasteful use of computing devices such as memory ,processor cycles etc..
3. Correctness – 
   A software product is correct, if the different requirements as specified in the SRS document have been correctly implemented.
4. Reusability – 
   A software product has good reusability, if the different modules of the product can easily be reused to develop new products.
5. Testability – 
   Here software facilitates both the establishment of test criteria and the evaluation of the software with respect to those criteria.
6. Reliability – 
   It is an attribute of software quality. The extent to which a program can be expected to perform its desired function, over an arbitrary time period.
7. Portability – 
   In this case, software can be transferred from one computer system or environment to another.
8. Adaptability – 
   In this case, software allows differing system constraints and user needs to be satisfied by making changes to the software.
9. Interoperability – Capability of 2 or more more functional units to process data cooperatively.

Program vs Software Product: 
 

1. A program is a set of instructions which is given to a computer in order to achieve a specific task whereas a software is when a program is made available for commercial business and is properly documented along with its licensing. Software=Program+documentation+licensing.
2. A program is one of the stages involved in the development of the software, whereas a software development usually follows a life cycle, which involves the feasibility study of the project, requirement gathering, development of a prototype, system design, coding and testing.
    

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