Review Requirement Fit Criteria (Process Notes 4.1)

The purpose of the requirement fit criteria is to set communicable limits that the people involved in the project can understand well enough to test each solution. Ask your testers to help with this process.

Does the formalized requirement or formalized system constraint have a requirement fit criterion that provides an unambiguous way of testing any eventual solutions to determine whether they conform with that fit criterion?

Some requirements are easier to quantify than others. Functional requirements are the easiest of all, because they are bounded by a tight context and because we have had much more experience in quantifying them.

Suppose we have a requirement for a customer to send us orders. We can specify exactly which data describes a customer, how many customers we have, and what the projected growth/attrition rate is. Thus we could say that the requirement fit criteria for a customer are that any solution must record all of the defined data values for the defined number of customers and that it must be able to cope with the defined projected growth.

Now suppose the requirement states that when a customer sends us an order, we must respond fast. This performance requirement does not have an unambiguous requirement fit criterion. It would be impossible to test a solution and determine whether it conforms to this requirement, because different people might interpret "fast" differently. Thus we need to quantify how fast is "fast." This step forces many questions out into the open. Does "fast" have a different value in different circumstances? Does "fast" have the same value for all customers or all types of orders? The idea is to arrive at a value, a range of values, or a statement that can be used to test the fit of eventual solutions to that requirement.

The more abstract the concept, the more difficult it is to come up with a specific value for a requirement fit criteria. Provided you have a requirement relevant to the context, however, it is always possible to up with a quality measurement that conforms to our definition.

Suppose a requirement says that the system's automated interfaces must be "easy to use." Now we need a requirement fit criteria for "easy to use." Remember: We are looking for criteria so that we can test whether a solution satisfies the requirement. In this case it's impossible to find a number, but we can still ask the question, "How will we know whether a given solution fits this requirement?" Perhaps we can agree that a test panel of novice users must be able to get an answer to a query of grade 3 complexity within five minutes of first encountering the product.

Raise a question about any requirement or system constraint that does not have a testable fit criterion.