Domain Semantics

Table of Contents

• Functions
  • Scene State Function
  • Scene Objects Function
  • Refine Operator Function

Domain semantics files specify the mapping between the task and motion layers in the particular planning domain.

Functions

Scene State Function

• Input: SCENE-GRAPH, CONFIGURATION
• Output: EXPRESSION-LIST

The state function maps the geometric scene to a task state. The return value is a list of expressions (implicitly and-ed) that define the state.

State expressions are represented as lists of operators and arguments in S-Expression format.

Expression Examples

The following table provides several examples of state expressions in customary infix notation, as PDDL and Lisp S-Expressions, and as Python lists.

Infix Expression	PDDL / Lisp S-Expression	Python List
a AND b	(and a b)	["AND", "a", "b"]
a OR b	(or a b)	["OR", "a", "b"]
(a OR b) AND c	(and (or a b) c)	["AND", ["OR", "a", "b"], "c"]
position(foo) = x	(= (position foo) x)	["=", ["POSITION", "foo"], "x"]

Python Expression List

Here is an example return value as a Python list:

[["=", ["POSITION", "block_a"], "front_table__0__0"],
 ["=", ["POSITION", "block_b"], "front_table__0__-2"],
 ["=", ["POSITION", "block_c"], "block_a"]]

S-Expression List

And here is the same return value as a Lisp S-Expression:

((= (POSITION "block_a") "front_table__0__0")
 (= (POSITION "block_b") "front_table__0__-2")
 (= (POSITION "block_c") "block_a"))

Scene Objects Function

• Input: SCENE-GRAPH
• Output: OBJECTS-LIST

The scene objects function returns the PDDL objects for the scene. The return value is a list where each element is another list beginning with the object type and followed by all objects of that type.

Examples

The following examples show the object lists objects "block_a", "block_b" and "block_c" of type "BLOCK", and "location_0", "location_1", and "location_2" of type "LOCATION".

Python Example

Here is an example return value as a Python list:

[["BLOCK", "block_a", "block_b", "block_c"],
 ["LOCATION", "location_0", "location_1", "location_2"]]

S-Expression

And here is the same value as an S-Expression:

((BLOCK "block_a" "block_b" "block_c")
 (LOCATION "location_0" "location_1" "location_2"))

PDDL Example

These example values correspond to the following PDDL :objects clause:

(:objects  "block_a" "block_b" "block_c" - block
           "location_0" "location_1" "location_2" - location)

Refine Operator Function

• Input: SCENE-GRAPH, CONFIGURATION, OPERATOR
• Output: PLAN

The refine operator function computes the motion plan instantiations of task operators.