Definition of Rule

Definition Last Updated 17-Dec-2015 12:51

A rule determines one state from another according to the results of applying particular criteria to the values of specified characteristics. Because capability is the fundamental type describing the evolution of states, a rule may be seen as an essential part of the description or specification of a capability; rules can have no effect without systems to give effect to them, i.e. to realise the capabilities they describe.

Scope

Rule is a defined term of Enterprise Architecture. Rule is a defined term of Business Analysis.

Discussion

Article Last Updated 17-Dec-2015 12:51

A rule may be described as a conditional statement, If P then Q, sometimes written1This notation is due to Gottlob Frege, see Turnstile Symbol at Wikipedia. as P ⊢ Q, where,

  • P represents a set of premises, which are criteria applied to particular values of specified attributes belonging to one or more entities (i.e. an initial state),
  • The symbol ⊢ states the truth of Q, i.e. says that Q is the case, and
  • Q represents an outcome, the collective (final) state of one or more entities which may or may not include those in the premises

i.e. a rule is an instruction for the assignment of values2A value is not limited to being a single thing (number or otherwise): values may also be ranges (as limits or distributions) or more general objects such as sets. according to the results of applying certain criteria to other values.

Since a change in an attribute value may modify a behaviour (i.e. an activity of an entity), application of a rule to such a triggering attribute may be used to control things, i.e. execution of the rule may start, stop, speed up, slow down or otherwise change one or more behaviours.

There are two kinds of rule3It is tempting to consider applying the classifications of Speech Acts, due to J. L. Austin and developed by John Searle but it does not seem strictly necessary today. Maybe tomorrow.: knowledge rules and manufacturing rules. Recall that a description may be true or false of something, e.g. it is False to say of dogs that they purr when stroked, but it is True of dogs that they wag their tails when happy.

A knowledge rule declares4The etymology of declare is Latin, declarare meaning variously to announce, declare, indicate, prove, show, etc. something – most of which do not actually guarantee that something is actually so. truth or falsehood, by establishing a relationship5See relationship for a detailed description of how this works. between something and a description of it.

A manufacturing rule takes – or creates a – relationship between something and a description and obtains truth or falsehood by assertion6Assert is an ideal choice for this since its root, the Latin verb asserere meaning to lay hands on, directly implies interaction with the world; assertion does thus have the power that declare does not to guarantee that something is actually so., i.e. by altering the thing itself to achieve the appropriate correspondence between the thing and the description.

Rules may be also be classified as descriptive and prescriptive rules, where descriptive is largely synonymous with knowledge rule, and prescriptive is a particular kind of manufacturing rule.

  • Prescriptive (i.e. normative) rules require that under specified conditions a performer or actor undertake, avoid undertaking, commence or cease from undertaking, etc. a particular action or behaviour, or do something in a particular manner. This is achieved by creating in the performer a state representing a self-referential rule, i.e. executing the rule “Thou shalt not covet they neighbour’s ass,” creates in rule “I shall not covet my neighbour’s ass.”
  • Descriptive rules, which assert the value of dependent attributes, usually as a matter of logical, mathematical or linguistic inference from the reference attributes, and values.

Examples

  • Prescriptive, normative: If the temperature of the CPU exceeds 95°C, reduce the CPU clock speed.
  • Knowledge, descriptive: If the temperature of the CPU exceeds 95°C, the CPU is too hot.

Prescriptive, normative: If the CPU is too hot, reduce the CPU clock speed.

Notes   [ + ]

1.This notation is due to Gottlob Frege, see Turnstile Symbol at Wikipedia.
2.A value is not limited to being a single thing (number or otherwise): values may also be ranges (as limits or distributions) or more general objects such as sets.
3.It is tempting to consider applying the classifications of Speech Acts, due to J. L. Austin and developed by John Searle but it does not seem strictly necessary today. Maybe tomorrow.
4.The etymology of declare is Latin, declarare meaning variously to announce, declare, indicate, prove, show, etc. something – most of which do not actually guarantee that something is actually so.
5.See relationship for a detailed description of how this works.
6.Assert is an ideal choice for this since its root, the Latin verb asserere meaning to lay hands on, directly implies interaction with the world; assertion does thus have the power that declare does not to guarantee that something is actually so.

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