SOAR

1
SOAR

• CIS 488/588
• Bruce R. Maxim
• UM-Dearborn

2
Behavior Modeling

• Production rules can be used to model
  problem-solving behavior
• Short term memory holds WM assertions
• Long term memory holds production rules
• Derived from protocol analysis (e.g. studying
  transcripts of recorded think out loud problem
  solving sessions)

3
Behavior Modeling

• State of knowledge
• what the subject knows
• Problem behavior graph
• trace of subject moving through states of
  knowledge
• Problem solving
• search through network of problem states

4
SOAR

• Starts with an initial situation and moves toward
  the goal state
• Establishes a preference net to determine
  rankings of various choices
• absolute preferences connect states to
  acceptable, rejected, best, and worst nodes
• relative preferences connect states to better,
  worse, and indifferent nodes

5
SOAR

• Preference labels and links are translated into
  dominance relations among states
• Dominance relations used to select next current
  state
• If goal state not found, process begins again
• SOAR does no conflict resolution, it fires all
  applicable rules
• Rules generally focus on replacing the current
  operator being used to discover states

6
SOAR Algorithm

• To determine the preferred state using the SOAR
  automatic preference analyzer
• Collect all states that are labeled acceptable
• Discard all acceptable states that are also
  labeled rejected
• Determine the dominance relations as follows
• State A dominates state B if there is a better
  link from A to B but no better link from B to A
• State A dominates state B if there is a worse
  link from B to A but no worse link from A to B
• A state labeled best, and not dominated by any
  other state, dominates all other states
• A state labeled worst, which does not dominate
  any other state, is dominated by all other states

7
SOAR Algorithm

• Discard all dominated states
• Select the next state from among those remaining
  as follows
• If only one other state remains, select it.
• Otherwise, if no states remain, select the
  current state, unless it is marked rejected
• Otherwise, if all states are connected by
  indifferent links,
• If the current state is one of the remaining
  states, keep it.
• Otherwise, select a state at random
• Otherwise, announce an impasse

8
Hello World Rule

• From Chapter 2 of Soar 8 Tutorial
• This rule writes "Hello World" and halts.
•  
• sp hello-world
• (state ltsgt type state)
• --gt
• (write Hello World)
• (halt)
•  

9
SOAR Syntax

• sp soar production
• Body of rule delimited by
• Rule name is hello-world
• --gt separates the if and then parts of a rule
  statement
• Conditions and actions delimited by ( )
• Identifiers a..z, 0..9, , -,
• Variables lt identifier gt

10
Working Memory

• Contains the dynamic information for SOAR
  entities
• Sensor data
• Calculations
• Current operators
• Goals
• Collections of WM elements describing the same
  entity are called objects

11
How does hello-world work?

• The first condition always starts with a state
• ltsgt is a variable capable of matching everything
• So the interpretation of
• (state ltsgt type state)
• is if I exist
• Every entity has a state attribute so the actions
  are carried out

12
SOAR Operator

• Can do things in either the real world or in the
  mind of the SOAR agent
• Operators have two basic parts
• Proposal rule used to determine when an operator
  can be applied
• Application rule that actually performs the work
  for the operator

13
Operator Proposal Rule

• From Chapter 3 of Soar 8 Tutorial
• This operator writes "Hello World" and halts.
•  
• sp proposehello-world
• (state ltsgt type state)
• --gt
• (ltsgt operator ltogt )
• (ltogt name hello-world)

14
Syntax

• (ltsgt operator ltogt )
• This action creates a preference for the new
  operator in WM
• The marks it as an acceptable preference
• (ltogt name hello-world)
• This action creates a working memory element that
  holds the name of the operator
• Variable scope is limited to a single rule

15
Operator Application Rule

• From Chapter 3 of Soar 8 Tutorial
• This operator writes "Hello World" and halts.
•  
• sp applyhello-world
• (state ltsgt operator ltogt)
• (ltogt name hello-world)
• --gt
• (write Hello World)
• (halt)

16
English Versions

• Propose hello-world
• If I exist propose hello-world operator
• Apply hello-world
• If hello-world operator is selected
• Then write Hello World and stop

17
SOAR Execution Cycle

• Propose operators (rules)
• Select operations (decision procedure)
• Apply operator (rules)
• Go to step 1

18
Eater Move-North

• Move-north operator
• From Chapter 4 of Soar 8 Tutorial
• Proposemove-north
• If I exist, then propose the move-north
• operator.
•  
• sp proposemove-north
• (state ltsgt type state)
• --gt
• (ltsgt operator ltogt )
• (ltogt name move-north)

19
Eaters Demo
20
Eater Move-North

• Applymove-north
• If the move-north operator is selected, then
• generate an output command to
• move north.
• sp applymove-north
• (state ltsgt operator ltogt
• io ltiogt)
• (ltiogt output-link ltolgt)
• (ltogt name move-north)
• --gt
• (ltolgt move ltmovegt)
• (ltmovegt direction north)

21
Syntax

• io ltiogt
• This adds a requirement for a match on the output
  before firing the rule
• It is getting the output link ltolgt that will
  allow Eater movement (but not continuous
  movement)

22
Fixing Eater Move-North

• Move-north operator
• From Chapter 5 of Soar 8 Tutorial
• Corrected so operator applies more than once.
• Proposemove-north
• If I am at some location, then propose the
• move-north operator. 
• sp proposemove-north
• (state ltsgt io.input-link.eater ltegt)
• (ltegt x ltxgt y ltygt)
• --gt
• (ltsgt operator ltogt )
• (ltogt name move-north)

23
Explanation

• The key change is eliminating the test for state
  and focus on non-persistent object attributes
• This sets the stage for a second operator
  instance selected
• We also need to create a second apply rule that
  removes the previous move command from WM

24
Application Rule 1

• Applymove-north
• If the move-north operator is selected, then
• generate an output command to
• move north.
• sp applymove-north
• (state ltsgt operator.name move-north
• io.output-link ltolgt)
• --gt
• (ltolgt move.direction north)

25
Application Rule 2

• Applymove-northremove-move
• If the move-north successfully performs a move
• command, then remove the command from the
• output-link
• sp applymove-northremove-move
• (state ltsgt operator.name move-north
• io.output-link ltolgt)
• (ltolgt move ltmovegt)
• (ltmovegt status complete)
• --gt
• (ltolgt move ltmovegt -)

26
Multiple Rule Processing

• In SOAR both the operator proposal and
  application phases can be expanded
• Multiple rules fire and retract in parallel until
  the system researches equilibrium or quiescence
• Consider the Move-to-Food eater (it can sense
  walls, food, and bonus food)

27
Move-to-Food

• Propose move-to-food
• If there is normal food in an adjacent cell then
  propose move in that direction
• Propose move-to-food-bonus-food
• If there is bonus food in an adjacent cell then
  propose move in that direction and allow operator
  selection to be random

28
Move-to-Food

• Apply move-to-food
• If move-to-food op selected then generate an
  output command
• Apply move-to-food-remove-move
• If move-to-food op is selected and there is a
  completed move or ltolgt then remove move command

29
Move to Food

• From Chapter 6 of Soar 8 Tutorial
• Proposemove-to-foodnormalfood
• If there is normalfood in an adjacent cell,
• propose move-to-food in the direction of that
• cell and indicate that this operator can be
• selected randomly the preference.
• sp proposemove-to-food
• (state ltsgt io.input-link.my-location.ltdirgt.con
  tent
• ltlt normalfood bonusfood gtgt)
• --gt
• (ltsgt operator ltogt )
• (ltogt name move-to-food
• direction ltdirgt)

30
Move to Food

• Applymove-to-food
• If the move-to-food operator for a direction is
• selected, generate an output command to move in
  that
• direction.
• sp applymove-to-food
• (state ltsgt io.output-link ltolgt
• operator ltogt)
• (ltogt name move-to-food
• direction ltdirgt)
• --gt
• (ltolgt move.direction ltdirgt)

31
Move to Food

• Applymove-to-foodremove-move
• If the move-to-food operator is selected,
• and there is a completed move command on the
  output
• link,then remove that command.
• sp applymove-to-foodremove-move
• (state ltsgt io.output-link ltolgt
• operator.name move-to-food)
• (ltolgt move ltmovegt)
• (ltmovegt status complete)
• --gt
• (ltolgt move ltmovegt -)

32
Generalized Move Operator

• Check for adjacent square
• Do not propose moving into a wall
• Look for normal or bonus food
• Avoid other eaters
• Note the use of list notation to simplify rule
  syntax
• ltlt .. list .. gtgt

33
Advanced Move Operator

• Avoids thrashing (moving back and forth between
  the same two cells)
• Has a preference for moving to bonus food when
  available
• The jump operator code can be merged with the
  advanced move operator to allow an eater to jump
  over a cell that does not contain a wall