Information Technology Reference
In-Depth Information
information by performing an evaluation . Finally, an object may perform
an action which is a prescription , creating a rule that constrains the future
behaviour of the community. Prescriptions provide a flexible and powerful
mechanism for changing the system's business rules at runtime, enabling its
dynamic adaptation to respond to business changes and new needs.
Expressing accountability for actions allows the party responsible for the
changes in the rules to be identified, which is something that fits well with the
deontic nature of enterprise policies, because the party must be authorized
in order to perform the prescription. These concepts can be used to express
various governance frameworks. We can see these mechanisms at work in the
PhoneMob example when a new contract is established with an organization
fulfilling the role of Customer. The contract may be enacted by clicking on
a button in some web page, but it is binding on the PhoneMob because the
organization has performed a delegation to the Chief Information Ocer,
who is the party taking responsibility for the information system that acts as
her agent in accepting the web interaction that enacts the agreement.
2.8
Quality of Service and Other Constraints
So far, the treatment of behaviour has concentrated on the sequence of
tasks to be performed | the so-called functional aspects of the processes.
However, we also need to be able to place constraints on various aspects of
the quality of performance, such as how quickly things are done, how low
the failure probability should be, or how good the security properties should
be. This typically involves decorating the basic behaviour, which is a set of
permitted event sequences, with conditions on what variations in performance
are allowed.
For example, there will be policies that arise from a service level agree-
ment between the PhoneMob and a VIP customer, such as obligations on the
PhoneMob to observe response times for repairs and, in the case of violations,
to provide compensation, such as arranging for replacement of a troublesome
user handset.
This is a complex issue because there are many dependencies between
the parties, and any quality guarantee asked from one community member is
contingent on proper behaviour by others. For example, a requirement that
the logistics provider shall deliver a shipment within 12 hours is contingent
on the receiving party being available to take delivery before the end of the
period. In general, any obligation placed on an object depends on guarantees
of support given by its environment.
The details of how such quality constraints are expressed depend on the
property being considered, and would take us beyond the scope of this topic,
