Software Requirements is a sub-field of Software engineering

Software engineering

Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, and the study of these approaches; that is, the application of engineering to software...

 that deals with the elicitation, analysis, specification, and validation of requirements for software.

The software requirement specification

Software Requirements Specification

-Organization of an SRS:A Software Requirements Specification – a requirements specification for a software system – is a complete description of the behavior of a system to be developed. It includes a set of use cases that describe all the interactions the users will have with the software. In...

(SRS) document generates all necessary requirements for project development. To derive the requirements we need to have clear and thorough understanding of the products to be developed. This is prepared after detailed communications with project team and the customer.

An SRS clearly defines the following:

1. External interfaces of the system: They identify the information which is to flow 'from and to' the system.
2. Functional and nonfunctional requirements of the systems. They stand for the finding of run-time requirements.
3. Design constraints

The SRS outline is given below:

1. Introduction
   1. purpose
   2. scope
   3. definitions,acronyms and abbreviations
   4. references
   5. overview
2. Overall Descriptions
   1. product perspective
   2. product functions
   3. user characteristics
   4. assumptions and dependencies
3. Specific requirements
   1. External interfaces
   2. functional requirements
   3. performance requirements
   4. logical database requirements
   5. Design constraints
   6. Software system attributes
   7. organizing the specific requirements
   8. additional comments
4. supporting information
   1. table of contents and index
   2. appendixes