Information Technology Reference
In-Depth Information
8.4
Conformance to Viewpoint Specifications
We explained earlier how conformance test results need interpretation to
identify the actions that are defined in the standard. Nowhere is this more
important than in the enterprise viewpoint, which deals with quite abstract
actions and events. We therefore conclude this chapter by looking at how this
mechanism works in more detail.
Consider an interaction performed by a specific role in an enterprise speci-
cation | perhaps the transfer of billing information from the Branch system
to the HQ system. This interaction should be observable at a reference point
positioned on the communications path between the two systems, such as the
HQ system's network access link. However, there is a big gap between the arc
in the activity diagram representing the enterprise behaviour and the optical
fluctuations on the access link.
Let us look first at the series of design steps involved in narrowing down
the requirements. Within the enterprise specification, we need to identify
the object that is playing the role that is being considered. The arc in the
enterprise behaviour can then be associated via some correspondences with
a transition in a state machine expressing the computational behaviour. In
fact, both the behaviour of the Branch system and the behaviour of the HQ
system will have such a transition, but, since we are focusing on the HQ system
in performing the tests, we will concentrate on its behaviour. Note, however,
that the transition may not be directly involved in a correspondence, but
might need to be inferred from correspondences involving the states it links;
even so, there is still a chain of logic pointing to it, which, in turn, identifies
a computational interaction.
The way this interaction is performed will depend on the selection of an
engineering template that satisfies the transparency requirements in the par-
ticular environment, and this will prescribe an appropriate message format,
protocol and series of message exchanges. How these exchanges are carried out
then depends on the implementable standards identified for communications
in the technology viewpoint. Each of these choices is recorded in the system's
documentation, either in the viewpoint specifications, the correspondences or,
for the last stages, by the implementer making statements within the IXIT
(see chapter 6).
The analysis of the results of a conformance test reverses this sequence (see
figure 8.4). First, knowledge of the communications standards in use allows
the physical measurements to be interpreted, yielding a bit stream and then
a series of raw messages. Knowledge of the protocols and formats in use lets
these be interpreted to identify the computational actions being performed
and the parameters they convey. It is common for monitoring tools in current
use to do this; anyone who has carried out a hand analysis of a binary dump
knows how valuable such tools are.
