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Common AI Architectures (GATE-561)

Dr.Çağatay ÜNDEĞER

InstructorMiddle East Technical University, GameTechnologies

Bilkent University, Computer Engineering

&

General ManagerSimBT Inc.

e-mail : cagatay@undeger.com

Game Technologies Program – Middle East Technical University – Fall 2009

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Outline• Introduction to AI Architectures• Entities, Attributes and Relations• Tasks, Actions, States and Events• Finite-State Machines• Hierarchical Finite-State-Machines

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AI Architecture

• A complete system architecture (AI engine) – That defines mechanizm of a percept-

reasoning-action cycle• For modeling autonomous entity

behaviors

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An Example AI Architecture

Percepts Actions

Environment

SeeingHearingSmellingTasting

Touching

MovingTalkingFiring

...

InferenceInterpretation

Conflict resolutionPlanning

...

Situation Awareness

Reactive Behaviours

Delibrative Behaviours

Action Selection

Reasoning

Short & Long Term Memory

Learning Rule Matching...

Known facts& Rules

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Entities

• Any kind of objects within an environment

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Entities

• Trees• Bushes• Rocks• Cars• Tanks• Bridges• Human beings• Animals• Houses

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Attributes

• Any kind of parameters describing properties of an entity

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Attributes• Tank

– Type– Coordinate– Orientation– Velocity– Damage– Gun 1

• Loaded• Number of munitions left

– Gun 2• Loaded• Number of munitions left

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Relations

• Any link between two entities, groups of entities or types of entities defining a fact

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Relations

• Ahmet is father of veli• Suzan is mother of veli• Mustafa, Kenan and Oya are friends• Iraq forces is an opponent of US forces• TSK and SSM are stakeholders• X may have a relation with Y

• Strike is an eagle• Eagle is a bird• Bird is an animal

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Tasks

• Any piece of work, – Which has been undertaken or attempted – By someone – To reach a desired goal

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Tasks

• Playing backgammon• Doing a project• Going to school• Performing surveillance• Managing an accident• Defending a town• Attacking a town

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Sub-Tasks

• Smaller pieces of work to be done in order to perform and complete a task

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Playing Backgammon

• Determining the first player• Doing your move• Waiting opponent’s move• Becoming happy• Becoming sad

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Doing a Project

• Generating a list of candidate topics• Selecting one of the topics• Determining requirements• Performing research on requirements• Preparing a design• Implementing • Testing• Documenting development• Writing users-manuals

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Going to School

• Remembering the location of school• Planing an initial path to school• Going to school through the path

– Replanning a path to school if required• Entering the school• Planing an initial path to the classroom• Going to the classroom through the path

– Replanning a path to classroom if required• Entering the classroom

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Performing Surveillance• Determining the surveillance start location• Determining the surveillance path• Going to surveillance start location

– Replanning a path to location– Replanning a path to location if required

• Moving through surveillance path– Replanning a surveillance path if required

• Looking around to detect any suspicious activity

• Examining suspicious activity (detection)• Reporting details of detection

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Managing an Accident

• Waiting a call• Answering a call• Getting accident information on call• Finding nearest hospital• Calling nearest hospital for an ambulance• Getting an ambulance aircraft if required

– Calling Turkish General Staff– Requesting an ambulance aircraft approval– Waiting for approval– Getting approval / reject– Organizing an ambulance aircraft– ....

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Actions

• A primitive (may be un-interruptable) work to be done in order to perform a task

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Actions

• Do a chess move• Do a forward step• Change direction• Hang up a phone• Send a fax• Say a statement to someone• Talk to someone• Engage a target• Fire a target• Throw a bomb• Give an order

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States

• A position in time.

• A specific situation/case/condition – Among a set of all possible situations a

system may be in.

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States

• Standing• Sitting• Walking• Running• Jumping• Talking• Defending• Attacking

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Events

• Something that happens in time.

• An action, occurrence or a condition that causes a state transition

• Thus in addition to actions, – An external or internal event may cause a

transition

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Events

Getting dress

Going to school

Going to classroom

Sleeping

States

Clock rang

Events

Dressing completed

School reached andDoor open

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Attributes vs States• Attributes of an entity can be considered as a part of its state

information as below.

• Tank– Coordinate– Orientation– Velocity– Damage– Gun 1

• Loaded• Number of munitions left

– Gun 2• Loaded• Number of munitions left

• But usually they are not used that way.

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Tasks vs States• Meanwhile performing a task;

– A system may be in one state (may have sub-states) and

– May transite from one state to another.

• In a time instant, a system may:– Be in one state or– Be in more than one sub-states in a set of

parallel tasks: –Moving somewhere–Talking at the same time–Looking around at the same time

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Tasks vs States

1. Remembering the location of school2. Planing an initial path to school3. Going to school through the path4. Entering the school5. Planing an initial path to the classroom6. Going to the classroom through the

path7. Entering the classroom

Staying

Walking

Running

Opening Door

Sitting

Task: Going to schoolStates

Sub-Tasks

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Actions vs States

• An action may move a system from one state to another state

• From “Waiting a call” to “Talking on phone”– By a “Hang up phone” action

• From “Moving randomly” to “Attacking someone” – By an “Engage an enemy” action

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Actions vs States

Staying

Walking

Running

Opening Door

Sitting

States

Stand up

Actions

Go to location slowly

Go to location fast

Open door

Stop

Sit down

Actions

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Actions vs States

• It is also possible and common to model actions as states.

• In that condition;– A state will either:

• Perform some action or• Be idle.

– Only events will cause transitions.

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Finite-State Machines (FSMs)

• Defined by a set of states and transitions between them.

• Transition from a state to another state is triggered by a change (event or action) in the environment.

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Finite-State Machines (FSMs)

• FSMs are used broadly in the video game industry. – Quake and Quake 2: a simple FSM system. – Warcraft III: a complex FSM system

• FSMs also have a large role outside of the video game industry. – For example, cars, airplanes, and robotics have

complex FSMs.

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Finite-State Machines (FSMs)

• Also called “State Transition Networks/Diagrams”

Wander

AttackEnemy

SearchEnemy

Spawn

see enemy

initial state

not see enemy

hear sound

not hear sound

see enemy

dead

reborn dead

dead

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Finite-State Machines (FSMs)

• An FSM has an entry (initial) state for starting the execution.

• After execution starts, events and/or actions cause state transitions.

• Each state may execute a code while;– Entering a state– Maintaining a state in every step and/or – Leaving a state

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A Sample

Initial state

Standing

Sitting

Walking

Running

Working

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Hierarchical Finite-State Machines

• When the number of states increases,– It becomes very complicated to define the

FSMs and– High probable to have some bugs !

• A solution is to ddefine some higher level states, and

• Refine the details of states hierarchically.

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A Sample

Start

Load weapon

Point at enemy

Fire

weaponloaded

weaponunloaded

weaponunloaded

weaponloaded

enemy engaged

weaponloaded

Sub-finite state machine

Wander

AttackEnemy

SearchEnemy

Spawn

see enemy

not see enemy

hear sound

not hear sound

see enemy

dead

reborn dead

dead

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Advantages

• Very fast to execute.• Expressive enough for simple behaviors.• Can create tools for non-programmers to

build behaviors.• Probabilistic transitions can be introduced to

make unpredictable transitions/behaviors.

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Disadvantages

• Number of states and arcs can grow very fast.• Easy to do errors in complex FSMs.• Difficult to;

– Put propositional representations such as:• Pick up the best weapon • Attack the closest enemy

– Count such as: • Wait until the third time I see the enemy,

then attack– Perform actions in parallel

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Disadvantages

• But they are still prefered in many games, and• They can be improved with some special

additions such as:– Parallel finite-state machines– Higher level scripts to perform complex

transitions