Goal:A Goal associates an Agent with a Situation.If a Goal instance is present in the
Agent’s working memory,then the Agent intends to bring about the Situation
referenced by the Goal.Some Goals are intrinsic to the agent’s identity,and are
derived from its purpose.These persist throughout the life of the Agent.Others are
transient tactical Goals.It is often useful to express the purpose in terms of a utility
function that associates’goodness values’with Situations.The target situation of the
Goal is then the one that is estimated to maximise utility(determined dynamically).
Note that the agent’s knowledge base needs to include’rules’governing assertion and
deletion of(tactical)Goals.One fairly standard rule would be to assert a Goal to
provide a given service whenever the Agent agrees with another Agent to do so.
Two other simple but important concepts used in MESSAGE are:
InformationEntity(an object encapsulating a chunk of information)and Message.
The agent-oriented concept of Message differs from the object-orient one in a number
of respects.In UML,a Message is a causal link in a chain of behaviour,indicating
that an Action performed by one object triggers an Action by another object.In
MESSAGE,a Message is an object communicated between Agents.Transmission of
a Message takes finite time and requires an Action to be performed by the Sender and
also the receiver.The attributes of a Message specify the sender,receiver,a speech
act(categorising the Message in terms of the intent of the sender)and the content(an
InformationEntity).
Agent
GoalRole
Information
Entity
Resource
Action
Service
Task
Perceives
Plays
Performs
Implements
Acquaintance
AimsToAchieve
Provides
ServiceTo
Describes
StateOf
DirectAction Communicative
ActionA
ffects
Fig.1.Agent centric MESSAGE concepts
Figure 1 gives an informal agent-centric overview of how these concepts are inter-
related,showing their relationship to the agent concept.A complete description of the
MESSAGE metamodel can be found in[5].