Information Technology Reference
In-Depth Information
defines a standard set of transparencies covering common distribution prob-
lems. These are:
Access transparency hides differences in representation and pro-
gramming model between different environments, allowing language-
independent distribution. Almost all popular middlewares provide ac-
cess transparency.
Failure transparency masks failures of objects or their supporting
environment; its provision usually involves some mechanism, such as
checkpointing or replication, which allows the recovery of the object's
internal state.
Location transparency involves the provision of object identifiers or
other names in a form that is independent of the physical location of the
resources concerned, so that there is a decoupling between application
structure and the physical configuration supporting it.
Migration transparency hides the fact that an object has been moved
from both its current and potential users. Thus, a management function
can move an object to a new platform without worrying about causing
errors elsewhere in the system.
Relocation transparency is concerned with preserving the binding of
interfaces. It involves the updating of bindings so that existing commu-
nications are not disrupted when an object moves.
Replication transparency hides the fact that a particular interface
is supported not by just a single object, but by a cooperating group
of objects in order, for example, to achieve increased performance or
availability.
Persistence transparency hides from an object and its users the ac-
tions a system manager may take to temporarily suspend and then
resume execution of an object; the state of an object, or a container
for a whole collection of objects (such as a cluster), may be moved to
some secondary storage to conserve resources, or to give the impression
of continuous availability following system crashes. When persistence
transparency is present, the application's state is nonvolatile, surviving
failures of the supporting platform.
Transaction transparency conceals a whole group of concurrency
and consistency measures needed to ensure that independent threads
of behaviour can share resources in an orderly way. The transparency
schema identifies groups of related actions, leaving to the infrastructure
the bringing into play of appropriate transactional and compensation
mechanisms.
