一貫性 
参考定義
IEEE std 830-1998 (Consistent)
Consistency refers to internal consistency. If an SRS does not agree with some higher-level document, such as a system requirements specification, then it is not correct.
Internal consistency
An SRS is internally consistent if, and only if, no subset of individual requirements described in it conflict.
The three types of likely conflicts in an SRS are as follows:
a) The specified characteristics of real-world objects may conflict. For example,
1) The format of an output report may be described in one requirement as tabular but in another as
textual.
2) One requirement may state that all lights shall be green while another may state that all lights
shall be blue.
b) There may be logical or temporal conflict between two specified actions. For example,
1) One requirement may specify that the program will add two inputs and another may specify that the program will multiply them.
2) One requirement may state that "A" must always follow "B," while another may require that "A and B" occur simultaneously.
c) Two or more requirements may describe the same real-world object but use different terms for that
object. For example, a program's request for a user input may be called a "prompt" in one requirement
and a "cue" in another. The use of standard terminology and definitions promotes consistency.
