NOTE - Examples of specialized groups are:
a) addressed group: a set of objects that are addressed in the same way.
b) fault group: a set of objects that have a common fault dependency. For example, it may be assumed that if a computer fails, all objects executing on that computer also fail;
c) communicating group: a set of objects where all the objects participate in the same sequence of interactions with their environment.
d) fault tolerant replication group: a communicating group whose purpose is to provide a certain level of tolerance against some faults.
The specification of a configuration may be static or may be in terms of the operation of dynamic mechanisms which change the configuration, such as binding and unbinding (see 13.4).
NOTE - A configuration can be expressed in terms of the concepts of concurrent composition. The process of composition generates an equivalent object for the configuration, at a different level of abstraction.
Every domain has a controlling object associated with it.
The controlling object can determine the identities of the collection of objects which comprises the associated domain. The controlling object may communicate with a controlled object dynamically or it may be considered to have communicated in an earlier epoch (see 10.5) of the controlling object. Generally, the controlling object is not a member of the associated domain.
NOTES
1 - In enterprise terms, various policies can be administered by the controlling object over the domain.
2 - Domains can be disjoint or overlapping.
3 - By definition, a domain is a group, but not vice versa.
4 - Examples of specialized domains are
| Domain | Member Class | Relationship | Controlling Class |
|---|---|---|---|
| Security domain | processing object | subject to policy set by | security authority object |
| Management domain | managed object | subject to policy set by | management domain object |
| Addressing domain | addressed object | address allocated by | addressing authority object |
| Naming domain | named object | name allocated by | name authority object |
10.4 Subdomain: A domain which is a subset of a given domain.
A change of epoch may be associated with a change in the type of the object, so as to support type evolution. Alternatively, a change of epoch may be associated with a phase in the behaviour of an object of constant type.
For a distributed system to function correctly, the objects composing its configuration must be consistent. Thus, as the whole system evolves through a series of epochs, the individual objects which interact must never be in epochs in which their behaviours are sufficiently different that their concurrent composition leads to a failure. This concept will support the formalization of concepts of version and extensibility.
NOTE - A specification language may need to express
a) the way epochs are labelled;
b) the sequence of epochs, and whether all objects need to pass through all members of the sequence;
c) the rules for deriving the epoch of a composition from the epochs of its objects, particularly for configurations and complete systems;
d) whether identity of the epoch of an object is necessarily part of the state of that object;
e) whether objects can negotiate on the basis of their current epoch identities;
f) the relation of epoch to the concepts of local and global time.
Significant classes of reference point are identified in ODP; details of these, and of the relationship of modelling to conformance, are given in clause 15.