OntologiesReasoningComponentsAgentsSimulations

Agent-OrientedAgent-OrientedKnowledge RepresentationKnowledge Representation

Jacques Robin

OutlineOutline

MOF2 and Metamodeling UML2 Active classes and objects UML2 Components UML2 Protocol state machines UML2 Profiles A UML2 Profile for Multi-Agent Systems (MAS) A simple MAS model using the profile

Meta-modeling and MOF2Meta-modeling and MOF2

Q: What is a meta-model? A: A base of structural meta-knowledge that defines the constructs

(vocabulary) and their possible relations (grammar) of the knowledge representation language used to specify an agent’s knowledge

It does not contain knowledge about the agent’s environment, only about the language that the agent uses to represent such knowledge

MOF2 key ideas: Reuse structural core of UML2 for meta-modeling purposes While a class diagram specifying knowledge about a given domain is

part of a UML model, a class diagram specifying constructs of a knowledge representation (or modeling) language is a MOF meta-model

The abstract constructs and concrete visual syntax of a UML domain model and MOF meta-model are the same, only the modeling purposes and levels are different

Meta-circularity: MOF2 is its own meta-model (the meta-meta-model)

MOF2 Meta-Models MOF2 Meta-Models vs.vs. BNF BNF GrammarsGrammars

Same purpose Advantages of MOF:

Abstract instead of concrete syntax (more synthetic) Visual notation instead of textual notation (clarity) Graph-based instead of tree-based (abstracts from any reader

order) Entities (classes) have internal structure and behavior (strings do

not) Relations include generalization and undirected associations

instead of only order Specification reuse through inheritance and package relationships

Additional advantages with OCL: OCL constraint apply equally well to meta-models than to models Allows expressing arbitrary complex logical constraints among

language elements (more expressive) Allows defining formal semantics without mathematical syntax

Simplified MOF2 Meta-Model of itselfSimplified MOF2 Meta-Model of itself

InstanceSpecification

Parameter*

Generalization

*

AssociationClass

AssociationClass

DataType

PrimitiveType Enumeration

Interface*

1..*Relationship

Relationship

NamedElement

Constraint

*

TypedElementType

Property

ValueSpecification

Classifier

Feature Classifier

RedefinableElement

*

Element

*

NamedElement

BehavioralFeature StructuralFeature

Operation

*

UML2 Active x Passive ObjectsUML2 Active x Passive Objects

Active objects Instances of active classes

Possess their own, continuous execution thread

Concurrent to other active objects

Exchange data with other active objects asynchronously through message passing

Does not wait for the other active object target of the message to respond to pursue its own processing

Can be pro-active: execute behavior on its own initiative without waiting to receive a request from another object

Passive (regular) objects Instances of passive (regular)

classes Share a single thread with the

other passive objects constituting a sequential application

Exchange data with other passive objects synchronously through method invocation

Interrupts its processing, waiting for an answer of the other passive object before pursuing its own processing

Purely reactive: execute behavior only as response to a method invocation request from another object

UML2 Active Classes and ObjectsUML2 Active Classes and Objects

UML2 classes can encapsulate other classes

Thus, UML2 objects can encapsulate other objects

UML 2.0 Component Meta-ModelUML 2.0 Component Meta-Model

Class

Component

EncapsulatedClassifier

StrcuturedClassifierpart *

required

**

provided

ConnectableElementConnectorEnd2..* *

Connector

*

Interface

Classifier

*

Property

Structural Feature

Type

Classifier

TypedElement

Association

PackagableElement

Port*

UML2 Components: Key DistinctionsUML2 Components: Key Distinctions

UML2 Component ClassesComponent Classes appearing in Class Diagrams together with UML2 Classes, Associations, Interfaces, Ports, Dependency and Realization Relationships

UML2 Component InstancesComponent Instances appearing in Object Diagrams together with UML2 Objects, Links, Ports and Connector Relationships

UML2 UML2 Component SpecificationComponent Specification diagram that, represents the component as a black box, describes only what the component does, i.e., its provided services

and externally visible states and what the component needs from its external environment, i.e.,

its required services. UML2 Component RealizationComponent Realization diagram that,

represents the component as a white box, describes how the component does what it does, by way of an internal assembly from lower granularity

components, classes and assoiciations that it encapsulates.

Component Class vs. Component Class vs. Standard OO Programming ClassStandard OO Programming Class

Component class: Medium granularity intermediate

between system and class, corresponding to that of a module, a library, an API or a package

Necessarily encapsulates behavior, possibly also data

Possesses meta-data describing its services and requirements to compose/assemble it with other components

Necessarily designed by contract by realizing and requiring interfaces

Relationships with other component classes: essentially horizontal clientship, possibly also encapsulating containment and conceptual generalization

Compiled independently of other components, allowing binary, source code language independent compatibility

Not necessarily object-oriented

OOP class: Fine grained unit Necessarily encapsulates data,

possibly also behavior Does not possess descriptive meta-

data Not necessarily designed by

contract Relationship with other classes:

essentially conceptual generalization, possibly also horizontal clientship and encapsulating containment

Compiled together with the other classes of a program, thus preventing binary, source code language independent compatibility

Component Class vs. Component Class vs. Module, Library, Package and APIModule, Library, Package and API

API: Ambiguous term, can mean only an interface specification or an interface

specification and its implementation A component class always means the latter

Modules, libraries, packages and APIs: Not independently deployable Single unit of compilation Source code language dependent Only encapsulates behavior not data No user interface nor testing interface No meta-data

Libraries and APIs: No conceptual generalization relationships No encapsulating containment relationships

Modules and Packages: Merely a source code structuring namespaces No instantiation as run-time entity

Component Instance Component Instance vs.vs. Object Object

Component Instance: Independently deployable At run time subject to service

invocation At deployment time subject to

composition/assembly Possesses meta-data accessible at

run time through access methods that describe its services and requirements

Possesses a user-interface for stand-alone deployment

Not necessarily object-oriented A server component instance can be

substituted by another one that conforms to its contract with no need to recompile or even to interrupt the client component instances

Client component code independent of server component deployment location

Object: Must be wrapped inside a program

to be executed Only subject to method invocation Two object that cooperate to

provide a service must be recompiled together to modify one of them

Client object method code dependent of server object method code deployment location

UML2 ComponentsUML2 Components

Instantiating a component class to create a component object is a complex process that involves: Instantiating of its encapsulated owned components, classes and

associations, and Assembling these instances together through connectors

Principles of component-based object-oriented representations: Recursive decomposition: components are internally assembled

from smaller and smaller ones down to those made of a single class Uniformity: everything is a component, including the entire system Locality: a given diagram shows only the part of the entire model

that is visible from the local perspective of a single <<subject component>>

Q: Why are UML2 components interesting for AI system engineering?

A: In essence, agents are UML2 active components

Agents as Active UML2 Components: Agents as Active UML2 Components: MAS Simulation Specification Class MAS Simulation Specification Class

DiagramDiagram

<<enumeration>>SimStateKind

runningstopped

<<interface>>Simulation

+run+stop

<<subject component>>Simulation

+state:SimStateKindSimAg SimEnv

Sim

Realization relationship:component realizes services provided by interface

Port: encapsulated classifier connection point with environment

<<subject component>>Simulation

+state:SimStateKind

Agents as Active UML2 Components: Agents as Active UML2 Components: MAS Simulation Realization Class DiagramMAS Simulation Realization Class Diagram

<<component>>Agent

SimAgSensors

Effectors

<<component>>Environment

SimEnvSensors

Effectors

SimAg SimEnv

<<enumeration>>AgPubStateKind

emptyinitialized

perceptReceivedactionSent

<<enumeration>>SimStateKind

runningstopped

<<enumeration>>EnvPubStateKind

emptyinitialized

perceptsSentactionsReceived

<<interface>>SimEnv

+create+terminate

+getEnvState():EnvPubStateKind

<<interface>>SimAg

+create+terminate

+getAgState():AgPubStateKind

Sim

Dependency relationship:component requires services

provided by interface to provide the services it itself realizes

Port for connection w/ sub-component

<<subject component>>:Simulation

Agents as Active UML2 Components: Agents as Active UML2 Components: MAS Simulation Realization Object MAS Simulation Realization Object

DiagramDiagram

<<component>>: Environment

Effectors

Sensors

Sim

<<component>>Ag1:Agent

SimAg

Sensors

Effectors

<<component>>AgN:Agent

SimAgSensors

Effectors

. . .

SimAg

SimAg

SimEnv

Agents as Active UML2 Components: Agents as Active UML2 Components: Agent Specification Class DiagramAgent Specification Class Diagram

<<subject component>>Agent

SimAg

Sensors

Effectors

<<component>>Environment

SimEnv

Effectors

Sensors

<<enumeration>>SimStateKind

runningstopped

<<component>>Simulation

+state:SimStateKindSimAg SimEnv

<<interface>>SimAg

+create+terminate

+getAgState():AgPubStateKind

Percept

Percept1 Percept2

<<interface>>Sensors

+receive1():Percept1+receive2():Percept2

<<interface>>Effectors

+send1(p:Percept1,,ag:Agent)+send2(p:Percept2.ag:Agent)

<<enumeration>>AgPubStateKind

emptyinitialized

perceptReceivedactionSent

Action

Action1 Action2

<<interface>>Sensors

+receive1(ag:Agent):Action1+receive2(ag:Agent):Action2

<<interface>>Effectors

+send1(ac:Action1)+send2(ac:Action2)

Sim

Agents as Active UML2 Components: Agents as Active UML2 Components: Agent Specification Object DiagramAgent Specification Object Diagram

<<component>>: Simulation

SimAg SimEnv

<<subject component>>:Agent

SimAgSensors

Effectors

<<component>>: Environment

SimEnvEffectors

Sensors

Sim

<<subject component>>:Agent

Agents as Active UML2 Components: Agents as Active UML2 Components: Agent Realization Class DiagramAgent Realization Class Diagram

SimAg<<interface>>

updateFromPredictedActionEffect

+update(o:AgSimModel,a:Action):AgSimModel

<<component>>ActionEffectPredictor

Sensors

Effectors

AgSimModel

SimModel

<<component>>BeliefReviser

<<interface>>updateFromPercept

+update(o:AgSimModel,p:Percept):AgSimModel

<<delegates>>

<<component>>ActionChooser

<<interface>>chooseAction

+choose(m:AgSimModel):Action<<delegates>>

<<subject component>>:Agent

Agents as Active UML2 Components:Agents as Active UML2 Components:Agent Realization Object DiagramAgent Realization Object Diagram

SimAg

Sensors

Effectors

m0:AgSimModel

<<delegates>>

<<component>>:ActionChooser

:Action

:Percept

<<component>>:BeliefReviser

<<delegates>>

m1:AgSimModel

m2:AgSimModel

<<component>>:ActionEffectPredictor

Agents as Active UML2 Components: Agents as Active UML2 Components: Environment Specification Class DiagramEnvironment Specification Class Diagram

<<subject component>>Environment

SimEnv

<<component>>Agent

<<enumeration>>SimStateKind

runningstopped

<<component>>Simulation

+state:SimStateKindSimAg SimEnv

<<interface>>SimEnv

+create+terminate

+getEnvState():EnvPubStateKind

Percept

Percept1 Percept2

<<interface>>Sensors

+receive1():Percept1+receive2():Percept2

<<interface>>Effectors

+send1(p:Percept1,,ag:Agent)+send2(p:Percept2.ag:Agent)

<<enumeration>>EnvPubStateKind

emptyinitialized

perceptsSentactionsReceived

Action

Action1 Action2

<<interface>>Sensors

+receive1(ag:Agent):Action1+receive2(ag:Agent):Action2

<<interface>>Effectors

+send1(ac:Action1)+send2(ac:Action2)

SimAg

Sensors

Effectors

Effectors

Sim

Agents as Active UML2 Components: Agents as Active UML2 Components: Environment Specification Object DiagramEnvironment Specification Object Diagram

<<component>>: Simulation

SimAg SimEnv

<<component>>Ag1:Agent

SimAgSensors

Effectors<<subject component>>

: Environment

SimEnvEffectors

Sensors

<<component>>AgN:Agent

SimAgSensors

Effectors

. . .

Sim

Agents as Active UML2 Components: Agents as Active UML2 Components: Environment Realization Class Environment Realization Class

DiagramDiagram<<subject component>>

Environment

+EnvPubState:EnvPubStateKind

SimAg<<component>>

Ramifier

<<interface>>updateFromRamifications

+update(o:EnvSimModel):EnvSimModel

Sensors

Effectors

EnvSimModel

SimModel

<<component>>DirectEffectUpdater

<<interface>>updateFromDirectEffects

+update(o:EnvSimModel,ac:Action):EnvSimModel

<<delegates>>

<<interface>>computeNewPercepts

+percept(o:EnvSimModel,a:Agent):Percept

<<component>>PerceptUpdater

<<delegates>>

<<subject component>>:Environment

Agents as Active UML2 Components: Agents as Active UML2 Components: Environment Realization Object Environment Realization Object

DiagramDiagram

SimAg

Sensors

Effectors

:Action

m0:EnvSimModel

<<component>>:Ramifier

<<delegates>>

:Percept

<<component>>:PerceptUpdater

m2:EnvSimModel

m1:EnvSimModel

<<component>>:DirectEffectUpdater

<<delegates>>

UML2 Common BehaviorsUML2 Common Behaviors

BehavioralFeature

Feature

Operation

TimeEvent

ValueSpecification

ChangeEvent

Class

Classifier

Signal Reception

Class

isActive = true

Interface

*

0..1

0..1

*0..1

*

SendSignalEvent

Event

ReceiveSignalEventSendOperationEvent

ReceiveOperationEvent

BehavioredClassifier

Classifier

methodBehavior

specification

ActivityInteraction StateMachine

0..1

Trigger

*

StructuralFeature

*

UML2 Protocol State MachinesUML2 Protocol State Machines

Specialization of state machines to specify interaction protocols between concurrent components, i.e., How the state S of component C restricts the operations Os

1, ... Osk

that another component can request C to execute What are the states S1, ... Sk, that result from the execution in S of

Os1, ... Os

k (respectively)

Useful for represent cooperation, competition and negotiation protocols among agents

Meta-model:

source

target

outgoing

incoming postCondition

preCondition

StateMachine

ProtocolStateMachine

State

Vertex ProtocalTransition Constraint

Operation

*

*

Pseudostate

kind:Pseudostatekind

<<enumeration>>PseudostateKind

initialjoinfork

junctionchoice

entryPointexitPointterminate

*1..*

Concrete transition syntax:[<pre-Condition>] <Operation> / <post-Condition>

UML2 Protocol State Machines: UML2 Protocol State Machines: ExamplesExamples

empty initialized

init()/create()/

perceptsReceived actionsSent

receive() send(action)/

AgentPSM {protocol}

empty initialized

init()/create()/

perceptsSent actionsReceived

send(agent1,percept1)/

receive(agentN/)

EnvironmentPSM {protocol}

send(agentN,perceptN)/

receive(agent1)/

... ...

PseudoState

PseudoState State

Operation

ProtocolTransition

UML2 ProfilesUML2 Profiles

Self-extension mechanism to customize UML2 towards: Specific application families (i.e., multi-agent simulations) Specific implementation platforms (i.e., EJB, .net, web services)

A profile is a set of stereotypes Concrete syntax: <<string>> and/or icon

Stereotypes are specializations of meta-classes from the UML2 meta-model

Package Class

Property Association

Profile

ProfileApplication*

**

meta-class

ExtensionStereotype*

Image

icon

ExtensionEnd*

UML2 Superstructure Meta-Model

UML2 Extension/Customization Language Meta-Model

MOF Meta-Model of a Simple Multi-Agent MOF Meta-Model of a Simple Multi-Agent Simulations Modeling Language (MASML)Simulations Modeling Language (MASML)

MAS2..*

EnvironmentAgent

Sensor Actuator

1..* 1..*

Percept1..*

AgentAction1..*

MAS

ReasoningComponent1..*

Agent

ReflexAgent ReflexComponent

ReflexAgent

ReasoningComponent

Sensor

Actuator1..*

1..*

AutomataAgentGoalBasedAgent

Goal

GoalInitializationComponent

GoalUpdateComponent

GoalBasedBehaviorStrategyComponent

ReasoningComponent

GoalBasedAgent

3..*

EnvironmentStateModel

ModelBasedBehaviorStrategyComponent

AgentAutomataAgent

EnvironmentStateModel

ModelInitializationComponent

PercpetInterpretationComponent

RamificationComponent

ModelBasedBehaviorStrategyComponent

ReasoningComponent

AutomataAgent

Actuator

Sensor4..*

1..*

MOF Meta-Model of a Simple Multi-Agent MOF Meta-Model of a Simple Multi-Agent Simulations Modeling Language (MASML)Simulations Modeling Language (MASML)

Agent

KBAgent KBComponent

KBAgent

ReasoningComponent

1..*

KnowledgeBase

PersistentKB VolatileKB

0..*

KBSentence1..*

1..*

ReflexAgent

ReflexKBAgent ReflexKBComponent

ReflexKBAgent

ReflexComponent

KBAgent KBComponent PersistentKB

ReflexKB

context ReflexKBComponent inv Volat ileKB.isEmpty()

AutomataKBAgent

AutomataAgent

AutomataKBAgent KBComponent

KBAgent EnvironmentStateModelKB

4..*

VolatileKB EnvironmentStateModel

4 ..*

GoalBasedKBAgent

GoalBasedAgent

GoalBasedKBAgent KBComponent

KBAgent GoalKB EnvironmentStateModelKB

6..*

VolatileKB Goal EnvironmentStateModel

4 ..*3 ..*

UML2 Profile for MASUML2 Profile for MAS

MASML Meta-Model UML2 Meta-Model

MAS

Environment

Agent

Sensor

Actuator

Percept

AgentAction

ReasoningComponent

EnvironmentStateModel

KnowledgeBase

KBSentence

Component

isActive = true

Component

Port

Signal

Model Package

PackagableElement

TypedElement

*