Information Technology Reference
In-Depth Information
responsibilities and infrastructure matters, such as interchange formats and
conversion responsibilities (see section 11.4).
Like any other community contract, a federation contract can include the
definition of policies, and these allow the management of the federation to
be carried out by changing some of the constraints placed on members dy-
namically during the federation's lifetime. The policy-setting behaviour will
define the process for making changes, and what say the various parties have
in agreeing to the changes.
Because of the loose coupling between federated organizations, it is quite
likely that either the basic behaviour or the policies applied will give rise at
some stage to conflict and inconsistency. It is therefore usual to find that a sig-
nificant amount of a federation contract deals with the handling of violations,
exceptions and compensation terms.
11.2 Interpreting and Sharing Information
One of the main issues in establishing a federation is the decision of
what the form of the communication between the various parties should be.
Whether we are talking about humans or automated systems, any commu-
nication of information between two entities depends on a basic shared level
of understanding between them. The receiver of a message needs to be able
to interpret it, recognizing the terms it contains and the implications of the
context resulting from their position in both the message and the broader
dialogue. Without this understanding, no communication can take place.
We can express this by saying that the communicating entities must share
a common ontology, so that they agree what categories of things exist and
can therefore be referred to. They must also share some understanding of the
grammar or structure of their communications. If there is a core agreement,
it can be used to exchange further rules and definitions so as to broaden the
scope of the exchanges, although the state of the art only allows fairly straight-
forward enhancements of machine communications. Humans are much more
flexible, and use many subtle clues from the local context to remove ambigu-
ity. This can be seen in the extensive use made of local context in natural
language, as in Susumu Kuno's [83] \Time ies like an arrow, fruit ies like
a banana," or of wider context needed to understand Noam Chomsky's [58]
\The police were ordered to stop drinking after midnight," with its four pos-
sible interpretations.
At present, we rely on the federation contract to give us an agreed core
grammar and ontology, to which suitable domain-specific packages can be
added to cover the exchange of other categories of information. One of the
thrusts of current interoperability research is to develop more flexible exten-
sion mechanisms for use in loosely coupled communication.
