検証容易性 
参考定義
IEEE std 830-1998 (Verifiable)
An SRS is verifiable if, and only if, every requirement stated therein is verifiable. A requirement is verifiable if, and only if, there exists some finite cost-effective process with which a person or machine can check that the software product meets the requirement. In general any ambiguous requirement is not verifiable.
Nonverifiable requirements include statements such as "works well," "good human interface," and "shall usually happen." These requirements cannot be verified because it is impossible to define the terms "good," "well," or "usually." The statement that "the program shall never enter an infinite loop" is nonverifiable because the testing of this quality is theoretically impossible.
An example of a verifiable statement is
Output of the program shall be produced within 20 s of event x 60% of the time; and shall be produced within 30 s of event x 100% of the time.
This statement can be verified because it uses concrete terms and measurable quantities.
If a method cannot be devised to determine whether the software meets a particular requirement, then that
requirement should be removed or revised.
