plansys2_msgs

Messages and service files for the ROS2 Planning System

Links
- Rosindex

README

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.

Messages

plansys2_msgs::msg::Action

Used to specify a PDDL action, with preconditions and effects defined by plansys2_msgs::msg::Tree.

plansys2_msgs::msg::ActionExecution

Used to establish a communication protocol between the action executors (implemented as behavior trees) and the action executor clients (user provided lifecyle nodes that perform the actions).

plansys2_msgs::msg::ActionExecutionInfo

Used to provide feedback regarding the execution status of each action execution client.

plansys2_msgs::msg::ActionPerformerStatus

Used to provide status feedback from an action executor client to the executor.

plansys2_msgs::msg::DurativeAction

Used to specify a PDDL durative action, with requirements and effects defined by plansys2_msgs::msg::Tree.

plansys2_msgs::msg::Knowledge

This message is not used internally by the system, but provides feedback to the user when a knowledge item is added, removed, or modified.

plansys2_msgs::msg::Node

The base node message used for creating PDDL construct trees. See discussion above for details.

plansys2_msgs::msg::Param

Used to define PDDL parameters and instances.

plansys2_msgs::msg::Tree

Consists of a list of plansys2_msgs::msg::Node and defines a PDDL construct tree. See discussion above for details.

Services

plansys2_msgs::srv::AddProblemGoal

Used to add a goal represented as a plansys2_msgs::msg::Tree to the problem expert.

plansys2_msgs::srv::AffectNode

Used to add, remove, or modify a predicate or a function represented as a plansys2_msgs::msg::Node.

plansys2_msgs::srv::AffectParam

Used to add or remove a problem instance represented as plansys2_msgs::msg::Param

plansys2_msgs::srv::ClearProblemKnowledge

Used to clear the problem instances, predicates, and functions.

plansys2_msgs::srv::ExistNode

Used to check for the existence of a predicate or function represented as a plansys2_msgs::msg::Node.

plansys2_msgs::srv::GetDomain

Returns the domain as a string.

plansys2_msgs::srv::GetDomainActionDetails

Given an action name and an optional list of parameters, returns an action (plansys2_msgs::msg::Action). If the optional parameter list is not empty it will be used to define the returned action parameters. Otherwise, auto-generated values will be used. The optional parameter list can be used to retrieve an instantiated plan action.

plansys2_msgs::srv::GetDomainActions

Returns a list of the domain action names.

plansys2_msgs::srv::GetDomainDurativeActionDetails

Given a durative action name and an optional list of parameters, returns a durative action (plansys2_msgs::msg::Action). If the optional parameter list is not empty it will be used to define the returned durative action parameters. Otherwise, auto-generated values will be used. The optional parameter list can be used to retrieve an instantiated plan action.

plansys2_msgs::srv::GetDomainName

Returns the domain name.

plansys2_msgs::srv::GetDomainTypes

Returns the domain types.

plansys2_msgs::srv::GetDomainConstants

Returns the domain constants of a type.

plansys2_msgs::srv::GetNodeDetails

Returns a predicate or function node represented as a (plansys2_msgs::msg::Node). When used with the domain expert client, only the name of the node needs to be provided. When used with the problem expert client, the full construct string must be provided.

plansys2_msgs::srv::GetOrderedSubGoals

Returns an ordered list of sub-goals where each sub-goal is represented as a plansys2_msgs::msg::Tree. The sub-goals are ordered according their start times as specified in the plan.

plansys2_msgs::srv::GetPlan

Returns a generated plan as a list of times, actions (represented as strings), and durations.

plansys2_msgs::srv::GetProblem

Returns the problem as a string.

plansys2_msgs::srv::GetProblemGoal

Returns the entire problem goal represented as a plansys2_msgs::msg::Tree.

plansys2_msgs::srv::GetProblemInstanceDetails

Given a parameter name, returns an instance represented as a (plansys2_msgs::msg::Param).

plansys2_msgs::srv::GetProblemInstances

Returns a list of problem instances where each instance is represented as a plansys2_msgs::msg::Param.

plansys2_msgs::srv::GetStates

Used to return a list of predicates or functions where each predicate or function is defined as a plansys2_msgs::msg::Node.

plansys2_msgs::srv::IsProblemGoalSatisfied

Specifies if the given goal, represented as a plansys2_msgs::msg::Tree, has been satisfied.

plansys2_msgs::srv::RemoveProblemGoal

Removes the problem goal, including all sub-goals.