無あいまい性 
参考定義
IEEE std 830-1998 (Unambiguous)
An SRS is unambiguous if, and only if, every requirement stated therein has only one interpretation. As a
minimum, this requires that each characteristic of the final product be described using a single unique term.
In cases where a term used in a particular context could have multiple meanings, the term should be included
in a glossary where its meaning is made more specific.
An SRS is an important part of the requirements process of the software life cycle and is used in design,
implementation, project monitoring, verification and validation, and in training as described in IEEE Std
1074-1997. The SRS should be unambiguous both to those who create it and to those who use it. However,
these groups often do not have the same background and therefore do not tend to describe software requirements
the same way. Representations that improve the requirements specification for the developer may be
counterproductive in that they diminish understanding to the user and vice versa.
Natural language pitfalls
Requirements are often written in natural language (e.g., English). Natural language is inherently ambiguous.
A natural language SRS should be reviewed by an independent party to identify ambiguous use of
language so that it can be corrected.
Requirements specification languages
One way to avoid the ambiguity inherent in natural language is to write the SRS in a particular requirements specification language. Its language processors automatically detect many lexical, syntactic, and semantic errors.
One disadvantage in the use of such languages is the length of time required to learn them. Also, many nontechnical users find them unintelligible. Moreover, these languages tend to be better at expressing certain types of requirements and addressing certain types of systems. Thus, they may influence the requirements insubtle ways.
Representation tools
In general, requirements methods and languages and the tools that support them fall into three general categories-object, process, and behavioral. Object-oriented approaches organize the requirements in terms of real-world objects, their attributes, and the services performed by those objects. Process-based approaches organize the requirements into hierarchies of functions that communicate via data ßows. Behavioral approaches describe external behavior of the system in terms of some abstract notion (such as predicate
calculus), mathematical functions, or state machines.
The degree to which such tools and methods may be useful in preparing an SRS depends upon the size and complexity of the program. No attempt is made here to describe or endorse any particular tool.
When using any of these approaches it is best to retain the natural language descriptions. That way, customers unfamiliar with the notations can still understand the SRS.
