Basic concepts in Requirements Analysis and Specification

Role of a system analyst

The analyst starts requirements gathering and analysis activity by collecting all information from the customer which could be used to develop the requirements of the system. He then analyzes the collected information to obtain a clear and thorough understanding of the product to be developed, with a view to removing all ambiguities and inconsistencies from the initial customer perception of the problem. The following basic questions pertaining to the project should be clearly understood by the analyst in order to obtain a good grasp of the problem:

• What is the problem?

• Why is it important to solve the problem?

• What are the possible solutions to the problem?

• What exactly are the data input to the system and what exactly are the data output by the system?

• What are the likely complexities that might arise while solving the problem?

• If there are external software or hardware with which the developed software has to interface, then what exactly would the data interchange formats with the external system be?

After the analyst has understood the exact customer requirements, he proceeds to identify and resolve the various requirements problems. The most important requirements problems that the analyst has to identify and eliminate are the problems of anomalies, inconsistencies, and incompleteness. When the analyst detects any inconsistencies, anomalies or incompleteness in the gathered requirements, he resolves them by carrying out further discussions with the end-users and the customers.

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 high-level functions {fi}. The functional view of the system . 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.

View of a system performing a set of functions

Nonfunctional requirements

• Nonfunctional requirements deal with the characteristics of the system which cannot 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.

Identifying functional requirements from a problem description

The high-level functional requirements often need to be identified either from an informal problem description document or from a conceptual understanding of the problem. Each high-level requirement characterizes a way of system usage by some user to perform some meaningful piece of work. There can be many types of users of a system and their requirements from the system may be very different. So, it is often useful to identify the different types of users who might use the system and then try to identify the requirements from each user’s perspective.

Here we list all functions {fi} that the system performs. Each function is considered as a transformation of a set of input data to some corresponding output data.

Function fi

Example:- Consider the case of the library system, where

 F1: Search Book function

Input: an author’s name

Output: details of the author’s books and the location of these books in the library

Book Function

So, the function Search Book (F1) takes the author's name and transforms it into book details.

 Functional requirements actually describe a set of high-level requirements, where each high-level requirement takes some data from the user and provides some data to the user as an output. Also, each high-level requirement might consist of several other functions.