Ontologies Reasoning Components Agents Simulations Agent-Oriented Knowledge Representation Jacques Robin

Outline  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 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 vs. BNF Grammars  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 itself InstanceSpecification Parameter * Generalization * Association Class AssociationClass DataType PrimitiveType Enumeration Interface * 1..* Relationship NamedElement Constraint * TypedElement TypeProperty ValueSpecification Classifier FeatureClassifierRedefinableElement * Element * NamedElement BehavioralFeature StructuralFeature Operation *

UML2 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 Objects  UML2 classes can encapsulate other classes  Thus, UML2 objects can encapsulate other objects

UML 2.0 Component Meta-Model Class Component EncapsulatedClassifier StrcuturedClassifier part * required * * provided ConnectableElementConnectorEnd 2..* * Connector * Interface Classifier * Property Structural Feature Type Classifier TypedElement Association PackagableElementPort *

UML2 Components: Key Distinctions Component Classes  UML2 Component Classes appearing in Class Diagrams together with UML2 Classes, Associations, Interfaces, Ports, Dependency and Realization Relationships Component Instances  UML2 Component Instances appearing in Object Diagrams together with UML2 Objects, Links, Ports and Connector Relationships  UML2 Component Specification  UML2 Component 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. Component Realization  UML2 Component 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. Standard 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. Module, 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 vs. 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 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 >  Q: Why are UML2 components interesting for AI system engineering?  A: In essence, agents are UML2 active components

Agents as Active UML2 Components: MAS Simulation Specification Class Diagram > SimStateKind running stopped > Simulation +run +stop > Simulation +state:SimStateKind SimAg SimEnv Sim Realization relationship: component realizes services provided by interface Port: encapsulated classifier connection point with environment

> Simulation +state:SimStateKind Agents as Active UML2 Components: MAS Simulation Realization Class Diagram > Agent SimAg Sensors Effectors > Environment SimEnv Sensors Effectors SimAg SimEnv > AgPubStateKind empty initialized perceptReceived actionSent > SimStateKind running stopped > EnvPubStateKind empty initialized perceptsSent actionsReceived > SimEnv +create +terminate +getEnvState():EnvPubStateKind > 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

> :Simulation Agents as Active UML2 Components: MAS Simulation Realization Object Diagram > : Environment Effectors Sensors Sim > Ag1:Agent SimAg Sensors Effectors > AgN:Agent SimAg Sensors Effectors... SimAg SimEnv

Agents as Active UML2 Components: Agent Specification Class Diagram > Agent SimAg Sensors Effectors > Environment SimEnv Effectors Sensors > SimStateKind running stopped > Simulation +state:SimStateKind SimAg SimEnv > SimAg +create +terminate +getAgState():AgPubStateKind Percept Percept1Percept2 > Sensors +receive1():Percept1 +receive2():Percept2 > Effectors +send1(p:Percept1,,ag:Agent) +send2(p:Percept2.ag:Agent) > AgPubStateKind empty initialized perceptReceived actionSent Action Action1Action2 > Sensors +receive1(ag:Agent):Action1 +receive2(ag:Agent):Action2 > Effectors +send1(ac:Action1) +send2(ac:Action2) Sim

Agents as Active UML2 Components: Agent Specification Object Diagram > : Simulation SimAg SimEnv > :Agent SimAg Sensors Effectors > : Environment SimEnv Effectors Sensors Sim

> :Agent Agents as Active UML2 Components: Agent Realization Class Diagram SimAg > updateFromPredictedActionEffect +update(o:AgSimModel,a:Action):AgSimModel > ActionEffectPredictor Sensors Effectors AgSimModel SimModel > BeliefReviser > updateFromPercept +update(o:AgSimModel,p:Percept):AgSimModel > ActionChooser > chooseAction +choose(m:AgSimModel):Action >

:Agent Agents as Active UML2 Components: Agent Realization Object Diagram SimAg Sensors Effectors m0:AgSimModel > :ActionChooser :Action :Percept > :BeliefReviser > m1:AgSimModel m2:AgSimModel > :ActionEffectPredictor

Agents as Active UML2 Components: Environment Specification Class Diagram > Environment SimEnv > Agent > SimStateKind running stopped > Simulation +state:SimStateKind SimAg SimEnv > SimEnv +create +terminate +getEnvState():EnvPubStateKind Percept Percept1Percept2 > Sensors +receive1():Percept1 +receive2():Percept2 > Effectors +send1(p:Percept1,,ag:Agent) +send2(p:Percept2.ag:Agent) > EnvPubStateKind empty initialized perceptsSent actionsReceived Action Action1Action2 > Sensors +receive1(ag:Agent):Action1 +receive2(ag:Agent):Action2 > Effectors +send1(ac:Action1) +send2(ac:Action2) SimAg Sensors Effectors Sim

Agents as Active UML2 Components: Environment Specification Object Diagram > : Simulation SimAg SimEnv > Ag1:Agent SimAg Sensors Effectors > : Environment SimEnv Effectors Sensors > AgN:Agent SimAg Sensors Effectors... Sim

Agents as Active UML2 Components: Environment Realization Class Diagram > Environment +EnvPubState:EnvPubStateKind SimAg > Ramifier > updateFromRamifications +update(o:EnvSimModel):EnvSimModel Sensors Effectors EnvSimModel SimModel > DirectEffectUpdater > updateFromDirectEffects +update(o:EnvSimModel,ac:Action):EnvSimModel > computeNewPercepts +percept(o:EnvSimModel,a:Agent):Percept > PerceptUpdater >

:Environment Agents as Active UML2 Components: Environment Realization Object Diagram SimAg Sensors Effectors :Action m0:EnvSimModel > :Ramifier > :Percept > :PerceptUpdater m2:EnvSimModel m1:EnvSimModel > :DirectEffectUpdater >

UML2 Common Behaviors BehavioralFeature Feature Operation TimeEvent ValueSpecification ChangeEvent Class Classifier SignalReception Class isActive = true Interface * 0..1 * * SendSignalEvent Event ReceiveSignalEvent SendOperationEvent ReceiveOperationEvent BehavioredClassifier Classifier method Behavior specification Activity Interaction StateMachine 0..1 Trigger * StructuralFeature *

UML2 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 O s 1,... O s k that another component can request C to execute  What are the states S 1,... S k, that result from the execution in S of O s 1,... O s k (respectively)  Useful for represent cooperation, competition and negotiation protocols among agents  Meta-model: source target outgoing incoming postCondition preCondition StateMachine ProtocolStateMachine State VertexProtocalTransition Constraint Operation * * Pseudostate kind:Pseudostatekind > PseudostateKind initial join fork junction choice entryPoint exitPoint terminate * 1..* Concrete transition syntax: [ ] /

UML2 Protocol State Machines: Examples emptyinitialized init()/create()/ perceptsReceivedactionsSent receive()send(action)/ AgentPSM {protocol} emptyinitialized init()/create()/ perceptsSent actionsReceived send(agent1,percept1)/ receive(agentN/) EnvironmentPSM {protocol} send(agentN,perceptN)/ receive(agent1)/... PseudoState State Operation ProtocolTransition

UML2 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: > and/or icon  Stereotypes are specializations of meta-classes from the UML2 meta-model PackageClass PropertyAssociation Profile ProfileApplication * * * meta-class Extension Stereotype * Image icon ExtensionEnd * UML2 Superstructure Meta-Model UML2 Extension/Customization Language Meta-Model

MOF Meta-Model of a Simple Multi-Agent Simulations Modeling Language (MASML) MAS 2..* EnvironmentAgent SensorActuator 1..* Percept 1..* AgentAction 1..* MAS ReasoningComponent 1..* Agent ReflexAgentReflexComponent ReflexAgent ReasoningComponent Sensor Actuator 1..* AutomataAgentGoalBasedAgent Goal GoalInitializationComponent GoalUpdateComponent GoalBasedBehaviorStrategyComponent ReasoningComponent GoalBasedAgent 3..* EnvironmentStateModel ModelBasedBehaviorStrategyComponent AgentAutomataAgent EnvironmentStateModel ModelInitializationComponent PercpetInterpretationComponent RamificationComponent ModelBasedBehaviorStrategyComponent ReasoningComponent AutomataAgent Actuator Sensor 4..* 1..*

MOF Meta-Model of a Simple Multi-Agent Simulations Modeling Language (MASML) Agent KBAgentKBComponent KBAgent ReasoningComponent 1..* KnowledgeBase PersistentKB VolatileKB 0..* KBSentence 1..* ReflexAgent ReflexKBAgentReflexKBComponent ReflexKBAgent ReflexComponent KBAgentKBComponent PersistentKB ReflexKB context ReflexKBComponent inv Volat ileKB.isEmpty() AutomataKBAgent AutomataAgent AutomataKBAgent KBComponent KBAgent EnvironmentStateModelKB 4..* VolatileKB EnvironmentStateModel 4..* GoalBasedKBAgent GoalBasedAgent GoalBasedKBAgent KBComponent KBAgentGoalKB EnvironmentStateModelKB 6..* VolatileKBGoal EnvironmentStateModel 4..*3..*

UML2 Profile for MAS  MASML Meta-Model  UML2 Meta-Model MAS Environment Agent Sensor Actuator Percept AgentAction ReasoningComponent EnvironmentStateModel KnowledgeBase KBSentence Component isActive = true ComponentPort Signal Model Package PackagableElement TypedElement *