What Is a Requirement?


A requirement is something the product must do or a quality it must have. A requirement exists either because the type of product demands certain functions or qualities or because the client wants that requirement to be part of the delivered product.

Functional Requirements

A functional requirement is an action that the product must take if it is to be useful to its users. Functional requirements arise from the work that your stakeholders need to do. Almost any actioncalculate, inspect, publish, or most other active verbscan be a functional requirement.

Functional requirements are things the product must do.


The product shall produce an amended de-icing schedule when a change to a truck status means that previously scheduled work cannot be carried out as planned.


This requirement is something that the product must do if it is to be useful within the context of the customer's business. In the preceding example, the customers for the product are the counties and other authorities that have responsibility for dispatching trucks to spread de-icing material on freezing roads.

Nonfunctional Requirements

Nonfunctional requirements are properties, or qualities, that the product must have. In some cases, nonfunctional requirementsthese describe such properties as look and feel, usability, security, and legal restrictionsare critical to the product's success, as in the following case:

Nonfunctional requirements are qualities the product must have.


The product shall be able to determine "friend or foe" in less than 0.25 second.


Sometimes they are requirements because they enhance the product:

The product shall be recognizable as an Atlantic Systems Guild product.


Sometimes they make the product usable:

The product shall be able to be used by travelers in the arrivals hall who do not speak the home language.


Nonfunctional requirements are usuallybut not alwaysdetermined after the product's functionality. That is, once we know what the product is to do, we can determine requirements for how it is to behave, what qualities it is to have, and how fast, usable, readable, and secure it shall be.

Constraints

Constraints are global requirements. They can be constraints on the project itself or restrictions on the eventual design of the product. For example, this is a project constraint:

Constraints are global issues that shape the requirements.


The product must be available at the beginning of the new tax year.


The client for the product is saying that the product is of no use if it is not available to be used by the client's customers in the new tax year. The effect is that the requirements analysts must restrict the requirements to those that deliver the maximum benefit within the deadline.

There may also be constraints placed on the eventual design and construction of the product, as in the following example:

The product shall operate on a 3G mobile telephone.


Providing that this is a real business constraintand not just a matter of opinionany solution that does not meet this constraint is clearly unacceptable. This leads us to say that constraints are simply another type of requirement.

Constraints are simply another type of requirement.





Mastering the Requirements Process
Mastering the Requirements Process (2nd Edition)
ISBN: 0321419499
EAN: 2147483647
Year: 2006
Pages: 371

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net