Information Technology Reference
In-Depth Information
11.5 Federating Type Systems
One way of simplifying the management of federated domains is to intro-
duce type repositories. The idea behind the type repository is to make all
the type definitions used in the domain accessible from a well-known service.
The same repository also registers the location of external type definitions,
indicating where the type repository for their local home domain can be ac-
cessed, and registers mapping information, in terms of subtype relationships,
so that potential users can reason about the types and deduce whether or
not an interceptor can be expected to convert them into a form that can be
understood locally.
The technical details of how this is done go beyond the scope of this topic,
but details of the ODP type repository can be found in ISO/IEC 14769:
The ODP Type Repository Function [15], which is also available as ITU-T
Recommendation X.960 . This standard laid the foundations upon which the
OMG later defined its specification for the Meta Object Facility [28].
11.6 Federating Identity
Another area of considerable practical importance is the federation of iden-
tity, which allows the creation of broadly based single sign-on schemes. Here
the aim is to support the establishment of distributed trust models and the
management of access tokens or pseudonyms. The federation approach to
these requirements is supported by technologies like WS-Federation [45] and
WS-Trust [47].
The general structure needed is very similar to the model underlying in-
teroperation. First, there needs to be an agreed conceptual framework for
expressing identity and trust, and a negotiated set of trust relationships be-
tween the various domain authorities. These may be either direct or indirect;
they are indirect if domains are linked by some third party, such as a trusted
peer or an acknowledged authority.
A federation community is then formed involving roles for the domains and
for the third-party broker if there is one. The federation contract defines the
behaviour used to export names with appropriate credentials, or to generate
linked tokens of pseudonyms. It expresses the properties that generated iden-
tities will have, such as their lifetime and any constraints on whether further
federation steps should be allowed. It also captures the way violations are sig-
nalled and the penalties associated with them. These days there may also be
obligations to disclose identity mappings on demand to the legal authorities,
so that criminal activity can be traced.
