10 Organizational concepts

10.1 <X> Group: A set of objects with a particular characterizing relationship <X>. The relationship <X> characterizes either the structural relationship among objects or an expected common behaviour of the objects.

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.

10.2 Configuration (of objects): A collection of objects able to interact at interfaces. A configuration determines the set of objects involved in each interaction.

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.

10.3 <X> Domain: A set of objects, each of which is related by a characterizing relationship <X> to a controlling object.

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.


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.

10.5 Epoch: A period of time for which an object displays a particular behaviour. Any one object is in a single epoch at one time, but interacting objects may be in different epochs at the time of interaction.

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.

10.6 Reference point: An interaction point defined in an architecture for selection as a conformance point in a specification which is compliant with that architecture.

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.

10.7 Conformance point: A reference point at which behaviour may be observed for the purposes of conformance testing.