message/uml 5

services.A service is the knowledge level analogue of an object’s operation.The
quality of autonomy means that an agent’s actions are not solely dictated by external
events or interactions,but also by its own motivation.We capture this motivation in
an attribute named purpose.The purpose will,for example,influence whether an
agent agrees to a request to perform a service and also the way it provides the service.
SoftwareAgent and HumanAgent are specialisations of Agent.
Organisation:An Organisation is a group of Agents working together to a common
purpose.It is a virtual entity in the sense that the system has no individual
computational entity corresponding to an organisation;its services are provided and
purpose achieved collectively by its constituent agents.It has structure expressed
through power relationships(e.g.superior-subordinate relationships)between
constituents,and behaviour/co-ordination mechanisms expressed through Interactions
between constituents.
Role:The distinction between Role and Agent is analogous to that between Interface
and(object)Class:a Role describes the external characteristics of an Agent in a
particular context.An Agent may be capable of playing several roles,and multiple
Agents may be able to play the same Role.Roles can also be used as indirect
references to Agents.This is useful in defining re-usable patterns.
Resource:Resource is used to represent non-autonomous entities such as databases or
external programs used by Agents.Standard object-oriented concepts are adequate for
modelling Resources.
The main types of Activity are:
Task:A Task is a knowledge-level unit of activity with a single prime performer.A
task has a set of pairs of Situations describing pre-and post-conditions.If the Task is
performed when a pre-condition is valid,then one can expect the associated post-
condition to hold when the Task is completed.Composite Tasks can be expressed in
terms of causally linked sub-tasks(which may have different performers from the
parent Task).Tasks are StateMachines,so that e.g.UML activity diagrams can be
used to show temporal dependencies of sub-tasks.
Interaction and InteractionProtocol:The MESSAGE concept of Interaction
borrows heavily from the Gaia methodology[6].An Interaction by definition has
more than one participant,and a purpose which the participants collectively must aim
to achieve.The purpose typically is to reach a consistent view of some aspect of the
problem domain,to agree terms of a service or to exchange to results of one or more
services.An InteractionProtocol defines a pattern of Message exchange associated
with an Interaction.
The internal architecture of an agent typically is based on one of several models
derived from cognitive psychology.MESSAGE is intended to be applicable to a
variety of agent cognitive architectures.However,without some basic abstract
reference model it is difficult to say anything meaningful.We suppose that the
architecture separates an inference mechanism from a knowledge base and a working
memory.The knowledge base contains fixed or slowly changing domain or problem-
solving knowledge in a declarative form.The working memory contains more
transient sensed or derived information.We view this working memory as an abstract
database holding instances of MentalStateEntities,and its contents define the Agent’s
mental state.For present purposes we focus on one type of MentalStateEntity:Goal.