message/uml 8

or other existing agents.Subsequent stages of refinement result in the creation of
models at level 1,level 2 and so on.
At level 0 the modelling process starts building the Organisation and the
Goal/Task views.These views then act as inputs to creating the Agent/Role and the
Domain Views.Finally the Interaction view is built using input from the other
models.The level 0 model gives an overall view of the system,its environment,and
its global functionality.The granularity of level 0 focuses on the identification of
entities,and their relationships according to the metamodel.More details about the
internal structure and the behaviour of these entities are progressively added in the
next levels.
In level 1 the structure and the behaviour of entities such as organisation,agents,
tasks,goals domain entities are defined Additional levels might be defined for
analysing specific aspects of the system dealing with functional requirements and non
functional requirements such as performance,distribution,fault tolerance,security.
There must be consistency between subsequent levels.In the MESSAGE project only
level 0 and level 1 have been considered.
Analysis Refinement strategies:Several strategies are possible for refining level 0
models.Organisation-centered approaches focus on analysing overall properties such
as system structure,the services offered,global tasks and goals,main roles,resources.
The agents needed for achieving the goals appear naturally during the refinement
process.Then co-operation,possible conflicts and conflict resolution may be
analysed.
Agent centred approaches focus on the identification of agents needed for
providing the system functionality.The most suitable organisation is identified
according to system requirements.Interaction oriented approaches suggest
progressive refinement of interaction scenarios which characterise the internal and
external behaviour of the organisation and agents.These scenarios are the source for
characterising task,goal,messages,protocols and domain entities.
Goal/task decomposition approaches are based on functional decomposition.
System roles,goals and tasks are systematically analyzed in order to determine the
resolution conditions,problem-solving methods,decomposition and failure treatment.
Task preconditions,task structures,task output and task post-condition may
determine what Domain Entities are needed.Goals and tasks must be performed by
agents playing certain roles.Consequently looking at the overall structure of goal and
tasks in the Goal/task view decisions can be made on the most appropriate agents and
organisation structure for achieving those goals/tasks.
The experience in MESSAGE shows that the different views of the system leave
the analyst free to choose the most appropriate strategy.In practice a combination of
refinement strategies with frequent loop-backs among them are used.The analysis
process might start with the OV,then switch to the AV and continue with the IV.The
results of the analysis of specific interaction scenarios may lead to reconsider part of
OV,and starting again refining and adapting OV constituents.