Information Technology Reference
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object for the party filling it, and abstracts away all aspects of the business
not involved in the federation (see figure 11.1). Each party should then only
depend on the abstract view of its peers captured by the role types found
in the contract; anything else may be changed without warning by the local
management.
«EV_Community»
phone service
federation
has role
has role
«EV_Role»
tour organizer
«EV_Role»
phone repairer
«EV_FulfilsRole»
«EV_FulfilsRole»
«EV_Object»
Factotum
«EV_Object»
PhoneMob
«EV_RefinesAsCommunity»
«EV_RefinesAsCommunity»
{Conforms to role type}
{Conforms to role type}
«EV_Community»
Travel Organization
«EV_Community»
Phone Repair
FIGURE 11.1: How organizations fill roles in a federation.
It is often helpful to use the concept of a domain to make issues of owner-
ship and accountability clear in these circumstances. A domain, in general, is
a set of objects with a characterizing relationship to some controlling object,
but the term can be used to express responsibility for resources, corresponding,
for example, to all or part of the area of authority of some partner. Defining
a suitable domain containing the resources to be committed to the federation
makes the scope of the contract clear.
The community behaviour of a federation covers two areas. First, it defines
the interactions between the parties that are necessary to achieve its objec-
tives. For example, Factotum sends a list of its customers to the PhoneMob,
requesting that they be given phone repair services for a specified period; later,
the PhoneMob bills for the cover and the actual repairs performed. Second,
the federation contract covers detailed responsibilities for establishing, main-
taining and terminating the federation. This covers organizational matters,
like periods of notice and penalties on withdrawal, but also defined technical
