-Usability refers to the ease 减轻 with which an application can be used. This is an
area in itself and there exist techniques for usability testing. Psychology 心理学 plays
an important role in the design of techniques for usability testing.
-Performance refers to the time the application takes to perform 执行 a requested
task 请求任务. It is considered as a
non-functional requirement
. It is specified in terms
such as ``This task must be performed at the rate of X units of activity in one second
on a machine running at speed Y, having Z gigabytes of memory."
这个任务必须以每秒 X 个单位的速度在运行速度 Y 的机器上执行，有 Z g 的内存
1.3 Requirements, behavior, and correctness
Requirements, behavior, correctness
Requirements leading to two different programs:
-Requirement 1: It is required to write a program that inputs two integers 整数 and
outputs the maximum of these.
-Requirement 2: It is required to write a program that inputs a sequence of integers
and outputs the sorted 排序 version of this sequence.
Requirements: Incompleteness 不完整性
Suppose that program max is developed to satisfy 满 足 Requirement 1. The
expected 预期 output of max when the input integers are 13 and 19 can be easily
determined to be 19.
Suppose now that the tester wants to know if the two integers are to be input to the
program on one line followed by a carriage return 回车, or on two separate lines with
a carriage return typed in after each number. The requirement as stated above fails
to provide an answer to this question.如上所述的要求不能提供这个问题的答案。
Requirements: Ambiguity 模棱两可
Requirement 2 is ambiguous. It is not clear whether the input sequence is to sorted
in ascending or in descending order. The behavior of sort program, written to satisfy
this requirement, will depend on the decision taken by the programmer while writing
sort.
Input domain 域 (Input space)
The set of all possible inputs to a program P is known as the input domain or input
space, of P.
Using Requirement 1 above we find the input domain of max
to be the set of all pairs of integers 整数 where each element in the pair integers is
in the range -32,768 till 32,767.
Using Requirement 2 it is not possible to find the input domain for the sort program.
Input domain (Continued)
Modified Requirement 2:
It is required to write a program that inputs a
sequence of integers and outputs the integers in this sequence sorted in either
