PlanSys2 Messages

Representing PDDL Expressions as Trees

PDDL expressions are conveniently represented as trees. To see this, consider the following PDDL expression.

(and (robot_at r2d2 millennium_falcon)(not (robot_at r2d2 death_star)))

The root node of the tree corresponds to the outer parentheses encompassing the “and” statement. The “and” statement then has two children. The first child corresponds to the predicate (robot_at r2d2 millennium_falcon) and the second child corresponds to the “not” expression (not (robot_at r2d2 death_star)). Similarly, the “not” expression has one child corresponding to the predicate (robot_at r2d2 death_star).

A tree node is often implemented as a simple class object of the form

class Node {
  public String name;
  public Node[] children;
}

Thus, the node contains the data relevant to the node as well as the links to its children. A tree is then stored as a list of nodes.

Representing PDDL Expressions with ROS Messages

PlanSys2 requires that the PDDL construct trees be passed back and forth between the various nodes of the system. To define a PDDL tree in ROS, we use two custom messages, plansys2_msgs/Tree and plansys2_msgs/Node. The contents of plansys2_msgs/Tree is simply an array of type plansys2_msgs/Node.

plansys2_msgs/Node[] nodes

The contents of plansys2_msgs/Node contains the data relevant to the node as well as links to its children.

uint8 node_type
uint8 expression_type
uint8 modifier_type

uint32 node_id
uint32[] children

string name
plansys2_msgs/Param[] parameters
float64 value
bool negate

The node_type defines the type of PDDL construct that the node represents. The following values are currently supported by PlanSys2.

uint8 AND = 1
uint8 OR = 2
uint8 NOT = 3
uint8 ACTION = 4
uint8 PREDICATE = 5
uint8 FUNCTION = 6
uint8 EXPRESSION = 7
uint8 FUNCTION_MODIFIER = 8
uint8 NUMBER = 9

When the node_type is EXPRESSION, the expr_type field is used to define the type of expression represented. The following expressions types are currently supported by PlanSys2.

uint8 COMP_GE = 10
uint8 COMP_GT = 11
uint8 COMP_LE = 12
uint8 COMP_LT = 13
uint8 ARITH_MULT = 14
uint8 ARITH_DIV = 15
uint8 ARITH_ADD = 16
uint8 ARITH_SUB = 17

When the node_type is FUNCTION_MODIFIER the modifier_type field is used to define the type of function modifier represented. The following function modifier types are currently supported by PlanSys2.

uint8 ASSIGN = 18
uint8 INCREASE = 19
uint8 DECREASE = 20
uint8 SCALE_UP = 21
uint8 SCALE_DOWN = 22

The node_id corresponds to the node’s location in the nodes list and takes on a value in the range [0, len(nodes)-1].

The children list specifies the locations, or node id’s, of the node’s children.

The name string and parameters list are used by predicate and function nodes, which are defined by a name and a list of parameters.

The value field is used by PDDL functions and stores a numeric value.

Finally, the negate field tracks whether the inverse truth value should be used. For example, if a NOT node is the parent of a PREDICATE node, then the PREDICATE node will have a negate value opposite that of the NOT node’s value.

Actions

plansys2_msgs::action::ExecutePlan

• Used to start and continuously monitor the execution of a plan.

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Changelog for package plansys2_msgs

3.0.1 (2025-06-22)

3.0.0 (2025-06-06)

• Multiple plans and replanning stability
• Add getProblemWithTimestamp to Problem Expert
• Service and logic for get multiple plans
• Replanning
• Executor basic replanning done
• Add support for ParamExpression and ConstExpression
• Support for existential preconditions
• add uint8 EXISTS = 10 to Node.msg
• Add support for derived predicates
• support for ParamExpression and ConstExpression
• add Derived.msg and GetDomainDerivedPredicateDetails.srv
• Fix CI after BT-CPP v4
• Remove cmake warning
• Add option to use planner node to validate domain in domain expert
• add Derived.msg and GetDomainDerivedPredicateDetails.srv
• Contributors: Francisco Martín Rico, Gustavo, Josh Zapf, Marco Roveri, Robodrome, Sebastian Castro

2.0.9 (2022-07-10)

2.0.8 (2022-05-04)

2.0.7 (2022-05-04)

2.0.6 (2022-05-03)

2.0.5 (2022-05-03)

2.0.4 (2022-05-03)

• Merge branch 'IntelligentRoboticsLabs:master' into master
• Contributors: Jake Keller

2.0.3 (2022-04-03)

2.0.2 (2022-04-03)

• Full supportr for (= _ _) PDDL constraints, added possibility to refer to constants, added initial test cases
• Add Status recency in performers
• Pddl domain (:constants ) handling and planning
• [domain_expert] GetDomainConstants service and tests
• [msgs] GetDomainConstants srv
• Contributors: Francisco Martín Rico, Jake Keller, Josh Zapf, Marco Roveri, Mostafa Gomaa

2.0.1 (2022-02-03)

• get-domain-name: Added service for retrieving domain name. Concatenating domain names when using multiple domains.
• Merge galactic-devel
• Contributors: Francisco Martín Rico, Josh Zapf

2.0.0 (2021-07-04)

1.0.10 (2021-07-03)

• Add ability to read in pddl problem files to plansys2 and a new AddProblem service to the plansys2_problem_expert. Adding problem_file node parameter to plansys2_problem_expert to load a single problem file at launch.
• ros2-plan-msg: Adding functions to plansys2_msgs/Knowledge message.
• ros2-plan-msg: Passing plan to executor to add further separation between plan creation and plan execution.
• pddl-tree-messages: Performing some minor cleanup.
• pddl-tree-messages: Merging master and resolving conflicts.
• Using custom behavior tree to enable action timeouts.
• pddl-tree-messages: Adding README to plansys2_msgs.
• pddl-tree-messages: Using ROS messages to define the PDDL construct trees.
• Plansys2_tests package
• Add GetOrderedSubGoals service to Executor, allowing executor clients to get the order in which sub-goals will be completed by the current plan.
• Update version
• Contributors: Alexander Xydes, Francisco Martín Rico, Josh Zapf

1.0.9 (2021-03-15)

1.0.8 (2021-03-12)

• Action execution refactoring
• Adding isGoalSatisfied function and unit tests to the problem expert api.
• Fixing typo in message name.
• Add support for numeric conditions and effects.
• Remove unused field
• Publish knownledge content
• Monitorization info
• fix minor typo
• Contributors: Alexander Xydes, Fabrice Larribe, Francisco Martin Rico, Josh Zapf

1.0.7 (2021-01-04)

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