Information Technology Reference
In-Depth Information
So far, we have concentrated on the interpretation of terms as having
intrinsic meaning, but there is another, equally important consideration, and
that is with the use of terms for referring to entities; that is to say, the
understanding of terms as names. The problem here is that, even within one
language community, there may be many local differences in the way things
are named. You may call your cat Fred, but in the house next door Fred may
be most immediately understood as the name of the householder. In such
cases, if I stand at my back door and call for Fred, I may get either the cat or
the neighbour.
Sorting the problem out lies at the heart of the so-called context-relative
approach to naming. This whole area is dealt with in detail in ISO/IEC 14771:
The ODP Naming Framework [16]. The standard gives a model of the passing
of names through a series of naming domains, explaining how the names should
be interpreted and transformed so that the communicating parties understand
them as references to the same thing, even though they have different forms
in each domain.
One particular topic described in the naming framework is the use of spe-
cial naming domains, or contexts, to support federation. These can be used
both to facilitate the intended communication within the federation and to
prevent unintended access by limiting the external visibility of local resources.
First, a partner in a federation can create a specific export context , which
contains the names of services it has agreed to make available. If all external
communication is restricted to be in terms of names in this context, any other
local services cannot be named, and so cannot be accessed by users outside
the organization.
To ease communication within the federation, a single shared naming con-
text, called the federation context , can be created as part of the federation
agreement. This context ensures that the various partners have a common set
of prexes for each others' resources, so that, in this form, their names are
never ambiguous.
Finally, an import context can be defined within an organization to
provide explicit control over the external services that local users can access.
In many cases, of course, an organization will forgo this level of control and
import the whole Internet naming structure into its local naming context, so
that all connected systems can be accessed by name, but there is a powerful
control mechanism available here for use if necessary.
11.3 The Basis of Interoperation
The full federation of separate organizations needs creation of a federation
contract which involves agreements in several viewpoints. Some aspects, given
in the following list, will be concerned with what the federation is for and how
