Similarly, the other basic domain concepts include Service,
Resource, Request and Constraints, which be shown
in BNF, although it should be noted that Constraint is a restriction
bonded with one or two simple resources. It may or
may not invoke some actions. In this research, the constraint
is only associated with simple resources for simplification
and clarification. If a restriction on aggregated resources
is needed, it has to be decomposed to a set of constraints of consisting simple resources. Restrictions on services should
be expressed as agreement provisions (ProvisionItem).