Requirements (PDDL 2.1)

Contributors: Adam Green,

Numeric Fluents

Support: High

Usage: High

    (:requirements :numeric-fluents)

Allows the inclusion of a :function block which represent numeric variables in the domain. e.g.

(:functions
    (battery-amount ?r - rover)
)

Note that this overrides the definition in PDDL1.2 in most planners.

Durative Actions

Support: High

Usage: High

    (:requirements :durative-actions)

Allows the use of durative-action in the domain definition. Durative actions are actions which have a duration they take to complete.

(:durative-action move
    :parameters (<arguments>)
    :duration (= ?duration 5)
    :condition (logical_expression)
    :effect (logical_expression)
)

Note that this does not imply :fluents

Durative Inequalities

Support: High

Usage: High

    (:requirements :durative-inequalities)

Allows the use of inequalities to express a duration. Rather than expressing that an action has a fixed length of time we can express that an action has a duration range using an inequality.

Continuous Effects

Support: Medium

Usage: High

    (:requirements :continuous-effects)

Allows the use of continuous effects on numerics within durative actions. Because durative actions take a period of time, we could model the change in a numeric value as some function of time. In reality support for this shaky. Linear functions are relatively easy for planners but non-linear effects are still an area of research.

Negative Preconditions

Support: Low

Usage: High

    (:requirements :negative-preconditions)

Allows the use of not in preconditions. The way some planners model actions mean they are not capable of handling negative preconditions. This is more an inconvenience that a serious design flaw as for every predicate their is an opposing predicate which is true when it’s false. I.e.

rover-charged and rover-not-charged are mutually exclusive. In the event where negative preconditions are not support we can introduce a second predicate which represents the negation of the predicate we want to express a negative precondition on.