Definition of Specification
Definition Last Updated 17-Dec-2015 12:51
A specification is a set of prescriptive rules1i.e. instructions for the assignment of values to attributes – properties, relationships and behaviours., which, if not defining something, typically expresses the simple idea that something matching the implied description is, in some appropriate way, good, praiseworthy, acceptable, etc. – even if rules express a negative (deprecation, prohibition, etc.): what matters is not what is done or not done, but whether the doing or omission was prescribed.
In practice, specifications are full of normative words and phrases (shall, shall not, should, should not, etc.) indirectly expressing the goodness etc. of particular values of specific characteristics or combinations thereof.
Permissive words and phrases, such as may, may not¸ typically express conditional normatives, particularly in the negative, e.g. “The noise of the engine may not exceed 120dBA unless the aircraft’s altitude is greater than 10,000m” which means “Engine noise shall be less than or equal to 120dbA at altitudes less than or equal to 10,000.”
Sometimes, however, permissives such as may indicate a free choice normatively associated with something else, e.g. “The colour of the body may be any colour, but if it is not black the advantages of the chosen non-black colour should be clearly stated.”
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