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| {{dablink|For other meanings of the same term, see [[fluent]]}}
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| In [[artificial intelligence]], a '''fluent''' is a condition that can change over time. In [[logic|logical]] approaches to reasoning about actions, fluents can be represented in [[first-order logic]] by [[Predicate (logic)|predicate]]s having an argument that depends on time. For example, the condition “the box is on the table”, if it can change over time, cannot be represented by <math>\mathrm{On}(\mathrm{box},\mathrm{table})</math>; a third argument is necessary to the predicate <math>\mathrm{On}</math> to specify the time: <math>\mathrm{On}(\mathrm{box},\mathrm{table},t)</math> means that the box is on the table at time <math>t</math>. This representation of fluents is used in the [[situation calculus]] using the sequence of the past actions in place of the current time.
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| A fluent can also be represented by a function, dropping the time argument. For example, that the box is on the table can be represented by <math>on(box,table)</math>, where <math>on</math> is a function and not a predicate. Converting predicates as functions in first-order logic is called [[Reification (knowledge representation)|reification]]; for this reason, fluents represented by functions are said to be reified. When using reified fluents, a separate predicate is necessary to tell when a fluent is actually true or not. For example, <math>HoldsAt(on(box,table),t)</math> means that the box is actually on the table at time <math>t</math>, where the predicate <math>HoldsAt</math> is the one that tells when fluents are true. This representation of fluents is used in the [[event calculus]], in the [[fluent calculus]], and in the [[features and fluents logic]]s.
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| Some fluents can be represented as functions in a different way. For example, the position of a box can be represented by a function <math>on(box,t)</math> whose value is the object the box is standing on at time <math>t</math>. Conditions that can be represented in this way are called ''functional fluents''. Statements about the values of such functions can be given in first order logic with equality using literals such as <math>on(box,t)=table</math>. Some fluents are represented this way in the [[situation calculus]].
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| ==See also==
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| * [[Event calculus]]
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| * [[Fluent calculus]]
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| * [[Frame problem]]
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| * [[Situation calculus]]
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| [[Category:Logic in computer science]]
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Latest revision as of 05:03, 13 March 2014
Oscar is how he's called and he totally enjoys this title. One of the very best issues in the globe for him is to collect badges but he is having difficulties to discover time for it. She is a librarian but she's always needed her personal business. Puerto Rico is where he and his wife reside.
Stop by my site ... http://www.lankaclipstv.com/blog/165665