Information Technology Reference
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in a quite abstract way, in terms of high-level interactions or messages. The
implementer needs to state how these interactions are supported, which may
involve reference to other standards or provision of additional pieces of speci-
fication.
The tester stimulates and observes behaviour at the conformance points.
The observations are necessarily at a very detailed level, in principle observing,
for example, electrical or optical signals being exchanged with the system un-
der test. These have to be interpreted in terms of the symbols they represent,
and then these in turn interpreted as complete messages, and so on. Eventu-
ally, this process results in detection of one of the atomic concepts from the
specification being tested (or an error in the implementation being detected
if the observations cannot be interpreted or make no sense). The tester then
knows that an event in the specification has occurred, and the sequence of
events detected so far (called a trace) can be checked against the behaviour
that the specification allows.
8.3 Types of Reference Point
The testing process can take a number of different forms, depending on
the nature of the reference points involved.
The RM-ODP identifies four
important kinds of reference point, as follows.
An interworking reference point is associated with some physical com-
munication channel, such as a network link or a connector between subsystems.
The physical signals passing between the communicating systems can be ob-
served. For instance, when a pair of protocol objects with SOAP interfaces are
bound together, an access cable to a network over which they communicate
can be specified as an interworking reference point.
A programmatic reference point indicates a software interface where
interactions can be observed for testing purposes. This implies some support
from the local system infrastructure to report events, such as calls to kernel or
middleware services, or provision for installation of some software monitoring
component, as might be provided by a modified class loader. For example, a
BEO may need to use an event notification service provided by an engineering
object within the same cluster. This interaction will be local and therefore
checks at the interface will involve use of a programmatic reference point.
A perceptual reference point is a point where the system interacts
with the real world. This may be via a keyboard and screen, or with some
more specialist device, like an ATM terminal, or through sensors and robotic
devices; there are many other examples. Testing at such a point involves
watching what happens when the system reports it is taking an action; if
the control system for a chemical plant reports a valve is being closed, can we
actually see this has in fact happened? Alternatively, a security audit function
 
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