Business Requirement Specification ( BRS ), Software Requirement Specification ( SRS ), Functional requirement Specification ( FRS )

Business Requirement Specification ( BRS ) : BRS contains the basic requirements of customer that are to be developed as software, project cost, schedule, target dates. It typcially expresses the broad outcomes the business requires rather than specific functions the system may perform.  Specific design elements are usually outside the scope of this document.

Software Requirement Specification ( SRS ) : SRS is implemented form of BRS. SRS is often referred as parent document of project  management document such as design specifications,statmnets of works ,software architecture specifications, testing and validation plans and documentation plans.The basic issues of SRS is what is the functionality(what is the s/w supposed to do)what are the external interfaces (how does the software interact with the user, other hardware, and other system software)performance(What is the speed of application ,recovery time ,response time, availability of various software functions)attributes(what is the portability, security, correctness etc )design constraints (OS environments, implementation of languages, database integrity and resource limits)

SRS contains the functional and non functional requirements only.

Functional requirement Specification ( FRS ) : FRS document provides the more detailed and described form of SRS.It contains the technical information and data needed to design the application. FRS define the what are software functionality will be and how to implement.