Restructured output format documentation once more and documented variables.
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# Output Format
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`plasp` 3 translates SAS and PDDL files into the same ASP fact format.
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`plasp` 3 translates SAS and PDDL files into a uniform ASP fact format.
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## Overview
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Essentially, `plasp`’s output format consists of *variables* that are modified by *actions* whose preconditions are fulfilled.
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`plasp`’s variables correspond to the multivalued variables in SAS.
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PDDL predicates are turned into Boolean variables to make the output format consistent.
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Actions are modeled exactly as PDDL actions and SAS operators.
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## In a Nutshell
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@ -14,11 +23,7 @@ type(type(switch)).
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constant(constant(a)).
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has(constant(a), type(switch)).
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% introduces another switch "constant(a)"
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constant(constant(b)).
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has(constant(b), type(switch)).
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% declares a variable "variable(on(X))" for each switch X
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% declares a variable "variable(on(X))" for switches X
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variable(variable(on(X))) :- has(X, type(switch)).
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% the variable may be true or false
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@ -30,91 +35,55 @@ action(action(turnOn(X))) :- has(X, type(switch)).
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precondition(action(turnOn(X)), variable(on(X)), value(on(X), false)) :- has(X, type(switch)).
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postcondition(action(turnOn(X)), effect(0), variable(on(X)), value(on(X), true)) :- has(X, type(switch)).
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% declares the action "action(turnOff(X))", which requires switch X to be on and then turns it off
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action(action(turnOff(X))) :- has(X, type(switch)).
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precondition(action(turnOff(X)), variable(on(X)), value(on(X), true)) :- has(X, type(switch)).
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postcondition(action(turnOff(X)), effect(0), variable(on(X)), value(on(X), false)) :- has(X, type(switch)).
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% initially, switch a is off and switch b is on
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% initially, the switch is off
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initialState(variable(on(constant(a))), value(on(constant(a)), false)).
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initialState(variable(on(constant(b))), value(on(constant(b)), true)).
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% in the end, switch a should be on and switch b should be off
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% in the end, the switch should be on
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goal(variable(on(constant(a))), value(on(constant(a)), true)).
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goal(variable(on(constant(b))), value(on(constant(b)), false)).
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```
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When translating SAS or PDDL problems, `plasp` structures the translated ASP facts into multiple sections, which are explained in the following.
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## Syntax and Semantics
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## Feature Requirements
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`plasp` structures the translated ASP facts into multiple sections, which are explained in the following.
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This section declares advanced features required by the input planning problem, such as conditional effects and axiom rules.
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Feature requirements may be used in meta encodings to warn about unsupported features.
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### Syntax
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syntax | description
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-------|------------
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`requiresFeature(<feature name>).` | declares the feature `<feature name>` to be required by the input problem
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Currently, feature requirements are only recognized with SAS problems.
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`plasp` supports the following feature requirements:
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SAS feature | description
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------------|------------
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`actionCosts` | actions have associated costs
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`axiomRules` | immediate actions are used, which are executed as soon as the preconditions are satisfied
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`conditionalEffects` | some effects of an action may have additional conditions
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### Example
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The following specifies that the input problem has the two requirements `actionCosts` and `conditionalEffects`.
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### Feature Requirements
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```prolog
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% requirements
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requiresFeature(actionCosts).
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requiresFeature(conditionalEffects).
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% declares a required feature
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requires(feature(<name>)).
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```
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## Types
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`plasp` recognizes and declares advanced features used by the input problem, such as conditional effects and [axiom rules](#axiom-rules) (currently only SAS).
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See the [full list of supported features](feature-requirements.md) for more information.
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This section specifies all object types used by the problem (only with PDDL and if typing is enabled).
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The feature requirement predicates may be used in meta encodings to warn about unsupported features.
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### Syntax
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syntax | description
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-------|------------
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`type(type(<type name>)).` | declares the type `type(<type name>)`
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### Example
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The following declares the type `type(block)` for later usage by the problem:
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### Types
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```prolog
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% types
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type(type(block)).
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% declares a <type>
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type(type(<name>)).
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% specifies <object> to be of type type(<name>)
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has(<object>, type(<name>)).
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```
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## Constants/Objects
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[Variables](#variables), [constants](#constants), and [objects](#objects) may be typed. Types are only available with PDDL and if typing is enabled.
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These two sections specify domain-specific (global) constants and problem-specific (local) objects (such as the blocks in a Blocks World puzzle).
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Constants and objects are not distinguished by `plasp`.
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### Syntax
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syntax | description
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-------|------------
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`constant(constant(<constant name>)).` | declares the constant or object `constant(<constant name>)`
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`has(constant(<constant name>), type(<type name>)).` | declares constant or object `constant(<constant name>)` to be of [type](#type) `type(<type name>)`
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### Example
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The following declares a constant `constant(a)` of [type](#types) `type(block)`:
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### Variables
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```prolog
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% objects
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constant(constant(a)).
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has(constant(a), type(block)).
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% declares a <variable>
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variable(variable(<name>)).
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% adds a <value> to the domain of a <variable>
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contains(<variable>, <value>).
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```
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With SAS, variable names are numbers starting at 0, `variable(<number>)`.
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SAS variables are inherently multivalued, which results in two or more values of the form `value(<SAS predicate>, <bool>)` for each variable.
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With PDDL, Boolean variables are created from the PDDL predicates.
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Variables ared named after the PDDL predicates, `variable(<PDDL predicate>).`
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Each variable contains exactly two values (one true, one false) of the form `value(<PDDL predicate>, <bool>)`.
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Note that with PDDL, variables and values are named identically.
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