by Dinesh Thakur

The development of software starts with the requirements document, which is also used to determine eventually whether or not the delivered software system is acceptable. It is therefore important that the requirement specification contains no error and specifies the client's requirement correctly.

 Further more due to the nature of the requirement specification phase, there is a lot of room for misunderstanding and committing errors, and it is quite possible that the requirements specification does not accurately represents the client's needs. The basic objective of the requirement validation activity is to ensure that SRS reflects the actual requirements accurately and clearly. A related objective is to check that the SRS documents is itself of "good quality" (Some desirable quality objectives are given later).


 

Many different  types of errors are possible , but the most common errors that occurs can be classified in four types : omission, inconsistency, incorrect fact, and ambiguity. Omission is a common error in requirements. In this type of error, some user requirements is simply not included in the SRS; the omitted requirement may be related to the behavior of the system, its performance, constraints, or any other factor.

 

Omission directly affects the external completeness of the SRS. Another common form of error in requirement is inconsistency. Inconsistency can be due to contradictions within the requirements themselves or due to incompatibility of the started requirements with the actual requirements of the client or with the environment in which the system will operate.

 

The third common requirement error is incorrect fact. Errors of this type occur when some facts recorded in the SRS are incorrect. The fourth common error type is ambiguity. Errors of this type occur when there are some requirements that have multiple meanings that is their interpretation is not unique.

 

Omission

Incorrect Fact

Inconsistency

Ambiguity

26%

10%

38%

26

 

In the errors detected in the requirement specification of the A-7 project (which deals with a real time flight control software) were reported. A total of about 80 errors were detected. Out of the which, about 23% were clerical in nature, of the remaining the distribution with error type was :

 

Omission

Incorrect Fact

Inconsistency

Ambiguity

32%

49%

13%

5%