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Language Specification - Detectable (DET) - Description

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A detectable is a declarative statement defining first which state changes an agent or object can detect and second what action results from detecting the state change.

Detecting facts is a two-phase process. In the first phase the agent or object detects the fact and the fact becomes a belief for the agent or object. No matter what the right hand side is in the form OA=V and OA=O the fact will become a belief for the agent or object. To make this behavior clearer, the detection condition may be stated without the equality and right hand side (OA) or the right hand side may be given as a wildcard character (OA=?). In the case of an ORO, the right hand side and truth value are also ignored in determining the matching facts and they also may be omitted from the condition (OR) or given as the wildcard character (OR?) to indicate that any fact with the specified relation and matching the left hand side should match the condition no matter what it has for a right hand side object or truth value.

In the second phase the beliefs of the agents or objects are matched with the detectable definition and if there is a positive match, the detectable action is executed. In contrast to the fact detection phase, the right hand side of a condition of the form OA=V, OA=O, or ORO is not ignored when matching beliefs. But if the right hand side of the condition is omitted or given as the wildcard ‘?’ any right hand side value or object is allowed in matching beliefs.

Note that these two phases are independent for agents and objects, i.e. regardless of whether the fact is present in the world, the second phase is performed. This means that if the agent or object has received a matching belief through a communication, the belief will trigger the action of the detectable.