Information Technology Reference
In-Depth Information
9.3 Transparencies and Viewpoints
The transparencies play an important role in the linkage between the man-
agement of infrastructure mechanisms in the engineering viewpoint and the
design constraints established in the computational, enterprise and informa-
tion viewpoints. The relationship between the computational and engineering
specifications is particularly significant because the computational design es-
tablishes the potential for distribution by specifying the constraints on the
behaviour of specific implementable objects. The enterprise and information
specifications impose broader, more generic, constraints on this computational
structure. However, the shift from the computational to the engineering view-
point introduces the properties of particular infrastructures and distribution
environments.
The computational designers mark their objects or interfaces to indicate
any special properties they are to have. The engineering specification then
defines a set of templates that give reusable solutions to the various distribu-
tion problems, together with the necessary rules for selecting the appropriate
templates to satisfy the computational requirement in whatever environment
actually applies. Instantiating the selected templates produces the various
components needed to provide a binding and hence a supporting channel with
the right properties.
client
object
mobile
server
relocator
migrator
object
locations
object
state
Trap anyservernot
founderror, try to
find at new location
and retry action.
Save object's state
and passivate it; re-
activate it at a new
location.
FIGURE 9.2: The supporting objects that are needed to provide migration
transparency.
Consider, for example, the provision of migration transparency for work
tickets in the PhoneMob system (see figure 9.2). The aim, from the com-
putational point of view, is for the object representing a repair task to be
