Information Technology Reference
In-Depth Information
(i) Kinds of interaction between an object and its environment.
Object
A. Interactions corresponding to
operations defined in the ob-
ject's interfaces.
B. Error terminations defined in
the object's interfaces.
C. Interactions reporting errors in
the environment, such as the
failure of other objects.
B
A
C
(ii) Consequence of requesting a transparency, as seen by the object.
Object
transparency
Interactions reporting the problems
masked by the transparency are hid-
den, but may be converted to other,
broader classes of error.
(iii) Infrastructure view of provision of the transparency.
Object
transparency
Infrastructure components catch er-
rors hidden by transparency and in-
voke corrective actions. If successful,
these result in the return of a normal
termination to the object.
Error
Trap
FIGURE 9.1: How transparencies change an object's environment.
transparency should be applied to a particular server. That is to say, the ap-
plication should not need to take any special action if the server object moves
to a new network location, as might, for example, be necessary to balance
load. The infrastructure's conguration control will assess the request. If the
server is indeed mobile, it will need to deploy extra components in the chan-
nel from this client to the server, perhaps to trap server-not-found exceptions,
search for the new server location and then reconfigure the communications
support to link to that location. On the other hand, it may be the case that
the server concerned is incapable of migration because it is closely coupled to
some physical resource, such as a huge data archive. If so, the infrastructure
