2.3.1 SOFTWARE REQUIREMENT SPECIFICATION

A) Concept 

After requirement analysis software requirement specification activity is coducted. Problem analysis does not focus on following issues like external behaviour,user interface behavior under erroneous situations.(eg. error in output),performance constraints,design constraints, standard compliance,recovery etc. but these things must be specified clearly in the SRS because the designer must know about these to properly design the system.
        The SRS is  written based on the knowlege acuired during analysis. As converting knowlege in to a structured document is not straightforword , secification itself is a major task, which is relatively independant.
   Parts of a SRS document

• The important parts of SRS document are:

􀂃 Functional requirements of the system
􀂃 Non-functional requirements of the system, and
􀂃 Goals of implementation
Functional requirements:-
􀂃 The functional requirements part discusses the functionalities required
from the system. The system is considered to perform a set of highlevel
functions {fi}. The functional view of the system is shown in fig.
3.1. Each function fi of the system can be considered as a
transformation of a set of input data (ii) to the corresponding set of
output data (oi). The user can get some meaningful piece of work done
using a high-level function.
on                                                  
{fi}
i1
i2
in
Input Output
Fig. 3.1: View of a system performing a set of functions
Nonfunctional requirements:-
􀂃 Nonfunctional requirements deal with the characteristics of the system
which can not be expressed as functions - such as the maintainability
of the system, portability of the system, usability of the system, etc.
􀂃 Nonfunctional requirements may include:
# reliability issues,
# accuracy of results,
# human - computer interface issues,
# constraints on the system implementation, etc.


Nonfunctional requirements:-
􀂃 Nonfunctional requirements deal with the characteristics of the system
which can not be expressed as functions - such as the maintainability
of the system, portability of the system, usability of the system, etc.
􀂃 Nonfunctional requirements may include:
# reliability issues,
# accuracy of results,
# human - computer interface issues,
# constraints on the system implementation, etc.

Goals of implementation:-
The goals of implementation part documents some general suggestions
regarding development. These suggestions guide trade-off among design goals.
The goals of implementation section might document issues such as revisions to
the system functionalities that may be required in the future, new devices to be
supported in the future, reusability issues, etc. These are the items which the
developers might keep in their mind during development so that the developed
system may meet some aspects that are not required immediately.