Computer software, or simply software, is a part of a computer system that consists of data or computer instructions, in contrast to the physical hardware from which the system is built. In computer science and software engineering, computer software is all information processed by computer systems, programs and data.

Software systems are abstract and intangible. They are not constrained by the properties of materials, governed by physical laws, or by manufacturing processes. This simplifies software engineering, as there are no natural limits to the potential of software.
Software engineering is a detailed study of engineering to the design, development and maintenance of software. Software engineering was introduced to address the issues of low-quality software projects. Problems arise when software generally exceeds timelines, budgets, and reduced levels of quality. It ensures that the application is built consistently, correctly, on time and on budget and within requirements. The demand of software engineering also emerged to cater to the immense rate of change in user requirements and environment on which application is supposed to be working.
The software development life cycle (SDLC) is a framework defining tasks performed at each step in the software development process. SDLC is a structure followed by a development team within the software organization. It consists of a detailed plan describing how to develop, maintain and replace specific software.
There are following six phases in every Software development life cycle model they are Requirement gathering and analysis, Design, Implementation or coding, Testing and Deployment Requirement gathering and analysis: Business requirements are gathered in this phase. This phase is the main focus of the project managers and stake holders. Design: In this phase the system and software design is prepared from the requirement specifications which were studied in the first phase. System Design helps in specifying hardware and system requirements and also helps in defining overall system architecture. The system design specifications serve as input for the next phase of the model. Implementation / Coding: On receiving system design documents, the work is divided in modules/units and actual coding is started. Since, in this phase the code is produced so it is the main focus for the developer. This is the longest phase of the software development life cycle. Testing: After the code is developed it is tested against the requirements to make sure that the product is actually solving the needs addressed and gathered during the requirements phase. During this phase all types of functional testing like unit testing, integration testing, system testing, acceptance testing are done as well as non-functional testing are also done. Deployment: After successful testing the product is delivered / deployed to the customer for their use. Maintenance: Once when the customers starts using the developed system then the actual problems comes up and needs to be solved
from time to time. This process where the care is taken for the developed product is known as maintenance
A software process model is a simplified representation of a software process. Each process model represents a process from a particular perspective, and thus provides only partial information about that process. The waterfall model, Incremental development and Reuse-oriented software engineering are software process models
The waterfall model takes the fundamental process activities of specification, development, validation, and evolution and represents them as separate process phases such as requirements specification, software design, implementation, testing, and so on.
Incremental development approach interleaves the activities of specification, development, and validation. The system is developed as a series of versions (increments), with each version adding functionality to the previous version.
Reuse-oriented software engineering approach is based on the existence of a significant number of reusable components. The system development process focuses on integrating these components into a system rather than developing them from scratch.
At last, it helps in understanding user conceptual models and development of better specifications as well as improvement in design languages and reusable code. It also helps in participatory design and interactive debugging and specification of interface and mockup to confirm specifications. In conclusion, software engineering is the most important field in information technology.

Thank you
Sudip Simkhada
Gongabu, Kathmandu