What do we mean by completeness and consistency of user requirement? Why is this difficult to achieve?

What do we mean by completeness and consistency of user requirement? Why is this difficult to achieve?

The functional requirements specification of a system should be both complete and consistent.


Completeness means that all services required by the user should be defined.

Consistency means that requirements should not have contradictory definitions.

In practice, for large, complex systems, it is practically impossible to achieve requirements consistency and completeness. One reason for this is that it is easy to make mistakes and omissions when writing specifications for complex systems. Another reason is that there are many stakeholders in a large system. A stakeholder is a person or role that is affected by the system in some way. Stakeholders have different—and often inconsistent—needs. These inconsistencies may not be obvious when the requirements are first specified, so inconsistent requirements are included in the specification. The problems may only emerge after deeper analysis or after the system has been delivered to the customer.