Glossary

This glossary is a derivative compilation of terms, including terminology from the Reference Model for Open Distributed Processing (RM-ODP) [ISO 96]. If the term is viewpoint specific, the viewpoint is indicated in brackets (for example "[ENTERPRISE]").

Abstraction:

The process of suppressing irrelevant detail to establish a simplified model, or the result of that process.

Access Transparency:

A distribution transparency which masks differences in data representation and invocation mechanisms to enable interworking of objects.

Action:

Something that happens. Every action of interest for modeling purposes is associated with at least one object.

Activity:

A single-headed directed acyclic graph of actions, where the occurrence of each action in the graph is made possible by the occurrence of all immediately preceding actions (i.e., by all adjacent actions which are closer to the head).

Architecture of a System:

A set of rules that defines the structure of a system and inter-relationships between its parts.

Behavior of an Object:

A collection of actions with a set of constraints on when they may occur. The specification language in use determines the constraints which may be expressed. Constraints may include, for example, serializability, nondeterminism, concurrency, or real-time constraints. A behavior may include internal actions. The actions that actually take place are restricted by the environment in which the object is placed.

Binder [Engineering]:

An engineering object in a channel that instantiates and maintains a distributed binding between interacting engineering objects.

Capsule [Engineering]:

A configuration of engineering objects forming a single unit for the purpose of encapsulation of processing and storage. Virtual machines and processes are examples of a capsule.

Channel [Engineering]:

A configuration of stubs, binders, protocol objects, and interceptors providing a binding (connection) between a set of interfaces to engineering objects, through which interactions can occur. Bindings that require channels are referred to as distributed bindings in the engineering language. Bindings that do not require channels (i.e., between objects in the same cluster) are referred to as local bindings.

Checkpoint [Engineering]:

An object template derived from the state and structure of an engineering object that can be used to instantiate another engineering object, consistent with the state of the original object at the time of checkpointing.

Class:

The set of all entities satisfying a type.

Cluster [Engineering]:

A configuration of engineering objects forming a single unit of deactivation, checkpointing, reactivation, recovery, and migration. A segment of virtual memory containing objects is an example of a cluster.

Community [Enterprise]:

A configuration of (enterprise) objects formed to meet an objective. The objective is expressed as a contract which specifies how the objective can be met.

Compliance:

The satisfaction of architectural constraints by a set of specifications.

Composition of Objects:

A combination of two or more objects yielding a new object, at a different level of abstraction. The characteristics of the new object are determined by the objects being combined and by the way they are combined. The behavior of the composite object is the corresponding composition of the behavior of the component objects. The composition of a collection of objects yields an equivalent object representing the composition. The behavior of this object is often referred to simply as the behavior of the collection of objects.

Computational Viewpoint:

The computational viewpoint partitions the system into objects which interact at interfaces. It enables distribution through functional decomposition of the system.

Configuration of Objects:

A collection of objects able to interact at interfaces. A configuration determines the set of objects involved in each interaction. The concept of interface and the related concept of interaction are defined terms. From these definitions, the concept of configuration can be seen to encompass not just a collection of objects, but also the way in which those objects are able to interact.

Conformance:

The satisfaction of specification constraints by a system or product implementation.

Conformance Point:

In a specification, a conformance point corresponds to an architectural reference point. A conformance point is where behavior may be observed for the purposes of conformance testing.

Contract:

An agreement governing part of the collective behavior of a set of objects. A contract specifies obligations, permissions, and prohibitions for the objects involved. The specifications of a contract may include:

• a specification of the different roles that objects involved in the contract may assume;

• the interfaces associated with the roles;

• Quality of Service (QoS) attributes;

• Quality of Protection (QoP) attributes;

• indications of duration or periods of validity;

• indications of behavior which invalidates the contract (preconditions, postconditions, invariants);

• live-ness and safety conditions.

Contractual Context:

The knowledge that a particular contract is in place and that a particular behavior of a set of objects is required. An object may be in a number of contractual contexts simultaneously; the behavior of that object is constrained by the intersection of the contractual agreements.

Decomposition of an Object:

The specification of a given object as a composition. As an example of the above definitions, an object, A, may be decomposed into a composition of objects, X and Y and Z, and, conversely, objects X and Y and Z may be composed into the single object, A.

Distribution Transparency:

An abstraction of the complexity of distribution processing from particular system users (such as application software developers). The standard distribution transparencies include: access, failure, location, migration, relocation, replication, persistence, and transaction. See the corresponding definitions.

Domain:

A set of objects, each of which is related by a characterizing relationship to a controlling object. Every domain has a controlling object associated with it. Examples of domains are Security domains and Management domains.

Dynamic Schema [Information]:

A dynamic schema is a specification of allowable state changes.

Engineering Viewpoint:

The engineering viewpoint focuses on object allocation, mechanisms, and functions (i.e., services) required to support distributed interaction between objects in the system.

Enterprise Viewpoint:

The enterprise viewpoint focuses on the purpose, scope, and policies (obligations, permissions, and prohibitions) of the system.

Entity:

Any concrete or abstract thing of interest. While in general the word entity can be used to refer to anything, in the context of modeling it is reserved to refer to things in the universe of discourse being modeled.

Environment of an Object:

The part of the model which is not part of that object. The set of actions associated with an object is partitioned into internal actions and interactions. An internal action always takes place without the participation of the environment of the object. An interaction takes place with the participation of the environment of the object.

Epoch:

A period of time for which an object displays a particular behavior.

Error:

Part of an object state which is liable to lead to failures; a manifestation of a fault in an object. Corrective action may prevent an error from causing a failure.

Failure:

The violation of a contract. The behavior specified in the contract is, by definition, the correct behavior. A failure is thus a deviation from compliance with the correct behavior.

Failure Transparency:

A distribution transparency which masks, from an object, the failure and possible recovery of other objects (or itself), to enable fault tolerance.

Fault:

A situation that may cause errors to occur in an object. Faults can be accidental, intentional, physical, man-made, internal, external, permanent, or temporary.

Federation [Enterprise]:

A community of domains.

Function:

Distributed processing functions are fundamental, widely applicable services that enable the construction of distributed processing systems. There are four standard categories of functions [ISO 96]:

• Management functions: object management, cluster management, capsule management, node management

• Coordination functions: event notification, checkpointing and recovery, deactivation and reactivation, group, replication, migration, engineering interface reference tracking, transaction

• Repository functions: storage, information organization, relocation, type repository, trading

• Security functions: access control, security audit, authentication, integrity, confidentiality, nonrepudiation, key management

Implementation [Technology]:

A process of instantiation whose validity can be subject to test.

Information Viewpoint:

The information viewpoint focuses on the semantics of information and information processing.

Instantiation of an Object Template:

An object produced from a given object template and other necessary information. This object exhibits the features specified in the object template.

Interaction Point:

A location where there exists a set of interfaces. A location is a position in both space and time.

Interceptor [Engineering]:

An engineering object in a channel located at a boundary between domains. An interceptor performs checks to enforce or monitor policies on permitted interactions between engineering objects in different domains. Interceptors perform transformations to mask differences in interpretation of data by engineering objects in different domains. An inter-subnetwork relay is an example of an interceptor, as are gateways and bridges.

Interface:

An abstraction of part of the behavior of an object. An interface comprises a set of interactions and a set of constraints.

Invariant:

A predicate that a specification requires to be true for the entire lifetime of a set of objects.

Invariant Schema [Information]:

A set of predicates on one or more information objects which must always be true.

Location Transparency:

A distribution transparency which masks the use of information about location in space when identifying and binding to interfaces.

Manager:

An engineering object which manages a collection (unit) of engineering objects. A cluster (capsule) manager is responsible for managing a single (capsule) cluster of engineering objects.

Migration Transparency:

A distribution transparency which masks, from an object, the ability of a system to change the location of that object. Migration is often used to achieve load balancing and reduce latency.

Mobility Schema:

A specification of constraints on the mobility of an object.

Name:

A term which refers to an entity in a given naming context. A name identifier is an unambiguous name in a given naming context.

Naming Context:

A relation between a set of names and a set of entities.

Node [Engineering]:

A configuration of engineering objects forming a single unit for the purpose of location in space. The node provides a set of processing, storage, and communications functions. Access to these functions is provided by a nucleus object. A computer and its software (operating system and applications) is an example of a node. A node can be a parallel computer under the control of a single operating system.

Nucleus [Engineering]:

An engineering object which coordinates processing, storage, and communications functions for other engineering objects within its node.

Object:

A model of an entity. An object is characterized by its behavior and, dually, by its state. An object is distinct from any other object. An object is encapsulated, i.e., any change in its state can only occur as a result of an internal action or as a result of an interaction with its environment. An object interacts with its environment at its interaction points.

Obligation:

A prescription that particular behavior is required. An obligation is fulfilled by the occurrence of the prescribed behavior.

Operation [Computational]:

An interaction between client and server objects. The syntax of an operation is usually defined by an operation signature (or function prototype).

Permission:

A prescription that a particular behavior is allowed to occur. A permission is equivalent to there being no obligation for the behavior not to occur.

Persistence:

The property that an object continues to exist across changes of contractual context of an epoch.

Persistence Schema:

A specification of constraints on the use of processing, storage, and communication functions.

Persistence Transparency:

A distribution transparency which masks, from an object, the deactivation and reactivation of other objects (or itself). Deactivation and reactivation are often used to maintain the persistence of an object when the system is unable to provide it with processing, storage, and communication functions continuously.

Policy:

A set of rules related to a particular purpose. A rule can be expressed as an obligation, a permission, or a prohibition. Not every policy is a constraint. Some policies represent an empowerment.

Postcondition:

A predicate that a specification requires to be true immediately after the occurrence of an action.

Precondition:

A predicate that a specification requires to be true for an action to occur.

Prohibition:

A prescription that a particular behavior must not occur. A prohibition is equivalent to there being an obligation for the behavior not to occur.

Proposition:

An observable fact or state of affairs involving one or more entities, of which it is possible to assert or deny that it holds for those entities.

Protocol Object [Engineering]:

An engineering object in a channel that communicates with other protocol objects in the same channel. Protocol objects achieve interaction between engineering objects which are in different clusters, capsules, and nodes.

Quality of Protection (QoP):

A set of security requirements on the collective behavior of one or more objects.

Quality of Service (QoS):

A set of quality requirements on the collective behavior of one or more objects.

Reference Point:

In an architecture, an interaction point designated for selection as a conformance point. The conformance point appears in a specification which is compliant with that architecture.

Refinement:

The process of transforming a specification into a more detailed specification. Specifications and their refinements typically do not coexist in the same system description.

Relocation Transparency:

A distribution transparency which masks relocation of an interface from other interfaces bound to it.

Replication Schema:

A specification of constraints on the replication, availability, and performance of an object.

Replication Transparency:

A distribution transparency which masks the use of a group of mutually behaviorally compatible objects to support an interface. Replication is often used to enhance performance and availability.

Role:

Identifier for a behavior, which may appear as a parameter in a template for a composite object, and which is associated with one of the component objects of the composite object.

Schema [Information]:

A specification of state, state changes, or constraints. The kinds of schema include: invariant schema, static schema, dynamic schema, mobility schema, persistence schema, and replication schema. See corresponding definitions.

Security—Access Control Function:

Prevents unauthorized interactions with an object.

Security Audit Function:

Provides monitoring and collection of information about security-related actions, and subsequent analysis of the information to review security policies, controls, and procedures.

Security—Authentication Function:

Provides assurance of the claimed identity of an object.

Security—Confidentiality Function:

Prevents the unauthorized disclosure of information.

Security—Integrity Function:

Detects and/or prevents the unauthorized creation, alteration, or deletion of data.

Security—Key Management Function:

Provides facilities for the management of cryptographic keys, including: key generation, registration, certification, deregistration, storage, archiving, and deletion.

Security—Nonrepudiation Function:

Prevents the denial by one object involved in an interaction of having participated in all or part of the interaction.

State of an Object:

At a given instant in time, the condition of an object that determines the set of all sequences of actions in which the object can take part.

Static Schema [Information]:

A specification of the state of one or more information objects at some point in time.

Stub [Engineering]:

An engineering object in a channel that interprets the interactions conveyed by the channel and performs any necessary transformations or monitoring based on this interpretation. Stubs are the engineering object in the channel which interface directly with the client and server objects.

Subtype:

An entity is a subtype of a given type if and only if its properties satisfy the predicate of the given type and other subtype-specific predicates.

System:

Something of interest as a whole or as comprised of parts. Therefore a system may be referred to as an entity. A component of a system may itself be a system, in which case it may be called a subsystem. For modeling purposes, the concept of a system is understood in its general, system-theoretic sense. The term system can refer to an information processing system but can also be applied more generally.

Technology Viewpoint:

The technology viewpoint focuses on the choice of technology in the system.

Template:

The specification of the common features of a collection of entities in sufficient detail that an entity can be instantiated using it. For example, an object template is the specification of the common features of a collection of objects in sufficient detail that an object can be instantiated using it. A object template is an abstraction of a collection of objects. A template may specify parameters to be bound at instantiation time. A standards specification containing interface bindings is a technology object template.

Transaction Transparency:

A distribution transparency which masks coordination activities among a configuration of objects to achieve consistency.

Transparency:

The property of hiding from a particular user the potential behavior of some parts of the system.

Type:

A predicate characterizing a collection of entities. An entity is of the type (or satisfies the type) if the predicate holds for that entity. Types needed are (at least) objects, interfaces, and actions. An entity may have several types and may acquire and lose types (for example: person, employee, homeowner).

Viewpoint Language:

Definitions of terminology, concepts, and rules for the specification of a system from a particular viewpoint. The standard viewpoint languages include: Enterprise Language, Information Language, Computational Language, Engineering Language, and Technology Language. See [ISO 96] Part 3 for details.

Viewpoint of a System:

A form of abstraction achieved using a selected set of architectural concepts and structuring rules, in order to focus on particular concerns within a system and its environment. Viewpoints often represent the perspective of a particular stakeholder or technical expert involved in the system. The viewpoint model addresses their issues and concerns. There are five standard viewpoints of a system: Enterprise, Information, Computational, Engineering, and Technology. See corresponding definitions.