Domain Partitioning Process

Divide the use cases into cohesive groups of one or more use cases 
that together describe a function of the system. 

Identify the objects that the use cases use and place the representative 
classes into the package/partition with the use cases. 

Identify the dependencies between the packages/partitions by evaluating 
the associations between the participating classes and the interactions that 
take place between the associated objects. 

Dividing the functionality of the system based on use cases is probably 
the most subjective part of the partitioning process. When you move on 
to the classes and interaction diagrams the partitions will become more 
clearly visible and may be tested for effectiveness.