Information Technology Reference
In-Depth Information
whose version we exchange, but it's like arguing with a foreign partner about
who pays the translator; we don't need to change the way we think, just be
sure the other side hears what they expect to hear."
\But how does that work if the infrastructures are dierent?" Nigel asked.
\You remember those interceptors in the engineering channel model? Well,
that's where the work is done. They are the translator, and they do whatever
jobs we find we need, subject to preserving our agreed high-level view. If the
middlewares are different, or the message formats, or any other detail, the
interceptor works its way up a process of interpretation to the point where
there is common agreement, and then works back down the stack translating
the common concepts into the other side's concepts."
\OK," said Marcus, \that sounds simple enough; let's just do it." \Well,
we'll nd out, won't we," said Eleanor, \ve gets you ten we aren't nished by
lunchtime." There were no takers.
11.1 How Does Interoperation Work?
The objective of a federation is to allow two or more separate organiza-
tions to cooperate while maintaining their fundamental independence. They
can each still go on doing what they want, managing their separate activities,
except that they must observe some minimum constraints in the narrow area
where these are needed to make the cooperation work. Generally, any of the
partners can opt out of the federation if it no longer matches their objectives,
although there may be some penalty, so as to compensate the other partners
if this happens.
Forming a federation is a particular case of forming a community, which
is the basic building block of the enterprise language. Like any community, a
federation is described by a contract | in this case, it is known as a feder-
ation contract . It also has an objective, representing the purpose for which
the cooperation was formed.
The necessary degree of independence is ensured because each of the par-
ties to the federation is an organization represented by its own community.
The federation community overlaps with these, so that the behaviour of the
complete system is the result of the composition of the constraints from the
federation with the constraints within each organization. Strictly speaking,
this is done by having the partners' communities ll roles in the federation
community. The definitions of the roles to be filled by the parties in the fed-
eration contract are made as abstract as possible, so as to avoid unnecessary
constraints on their ongoing activities. Remembering that a role is a formal
parameter to be instantiated by some object, it is clear that the role type
constrains the type of the object that can fulfil it. In this case, the federation
role type is significantly less detailed than the object type of the community
