1、INTERNATIONAL ISO/IEC STANDARD 10746-2 First edition 1996-09-I 5 Information technology - Open Distributed Processing - Reference Model: Foundations Technologies de /information - Traitement distribu6 ouvert - Mod b) the structure of distributed systems which claim compliance with the Reference Mode
2、l (the configuration of the systems); c) the concepts needed to express the combined use of the various standards supported; d) the basic concepts to be used in the specifications of the various components which make up the open distributed system. 2 Normative references The following Recommendation
3、s and International Standards contain provisions which, through reference in this text, constitute provisions of this Recommendation I International Standard. At the time of publication, the editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agre
4、ements based on this Recommendation I International Standard are encouraged to investigate the possibility of applying the most recent edition of the Recommendations and Standards listed below. Members of IEC and IS0 maintain registers of currently valid International Standards. The Telecommunicatio
5、n Standardization Bureau of the ITU maintains a list of currently valid ITU-T Recommendations. 2.1 Identical Recommendations I International Standards - ITU-T Recommendation X.903 (1995) I ISO/IEC 10746-3:1996, Znfonnarion technology - Open distributed processing - Reference Model: Architecture. 3 D
6、efinitions For the purposes of this Recommendation I International Standard, the following definitions apply. 3.1 Definitions from other Recommendations I International Standards There are no definitions from other Recommendations I International Standards in this Recommendation I International Stan
7、dard. 3.2 Background definitions 3.2.1 distributed processing: Information processing in which discrete components may be located in different places, and where communication between components may suffer delay or may fail. 3.2.2 ODP standards: This Reference Model and those standards that comply wi
8、th it, directly or indirectly. 3.2.3 open distributed processing: Distributed processing designed to conform to ODP standards. 3.2.4 ODP system: A system (see 6.5) which conforms to the requirements of ODP standards. ITU-T Rec. X.902 (1995 E) 1 ISO/IEC 10746-2 : 1996 (E) 3.2.5 information: Any kind
9、of knowledge, that is exchangeable amongst users, about things, facts, concepts and so on, in a universe of discourse. Although information will necessarily have a representation form to make it communicable, it is the interpretation of this representation (the meaning) that is relevant in the first
10、 place. 3.2.6 data: The representation forms of information dealt with by information systems and users thereof. 3.2.7 viewpoint (on 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 syste
11、m. 4 Abbreviations For the purposes of this Recommendation I International Standard, the following abbreviations apply: ODP Open Distributed Processing OS1 Open Systems Interconnection PIGS Protocol Implementation Conformance Statement PIXIT Protocol Implementation Extra Information for Testing RM-O
12、DP Reference Model of Open Distributed Processing TP Transaction Processing 5 Categorization of concepts The modelling concepts defined in this Recommendation I International Standard are categorized as follows: a) Basic interpretation concepts: Concepts for the interpretation of the modelling const
13、ructs of any ODP modelling language. These concepts are described in clause 6. b) Basic linguistic concepts: Concepts related to languages; the grammar of any language for the ODP Architecture must be described in terms of these concepts. These concepts are described in clause 7. c) Basic modelling
14、concepts: Concepts for building the ODP Architecture; the modelling constructs of any language must be based on these concepts. These concepts are described in clause 8. d) Specification concepts: Concepts related to the requirements of the chosen specification languages used in ODP. These concepts
15、are not intrinsic to distribution and distributed systems, but they are requirements to be considered in these specification languages. These concepts are described in clause 9. e) Structuring concepts: Concepts that emerge from considering different issues in distribution and distributed systems. T
16、hey may or may not be directly supported by specification languages adequate for dealing with the problem area. Specification of objects and functions that directly support these concepts must be made possible by the use of the chosen specification languages. These concepts are described in clauses
17、10 to 14. f) Conformance concepts: Concepts necessary to explain the notions of conformance to ODP standards and of conformance testing. These concepts are defined in clause 15. ITU-T Recommendation X.903 I ISO/IEC 10746-3 uses the concepts in this Recommendation I International Standard to specify
18、the characteristics for distributed processing to be open. It is organized as a set of viewpoint languages. Each viewpoint language refines concepts from the set defined in this Recommendation I International Standard. It is not necessary for all viewpoint languages to adopt the same notations. Diff
19、erent notations may be chosen as appropriate to reflect the requirements of the viewpoint. These notations may be natural, formal, textual or graphical. However, it will be necessary to establish correspondences between the various languages to ensure overall consistency. 6 Basic interpretation conc
20、epts Although much of the ODP Architecture is concerned with defining formal constructs, the semantics of the architectural model and any modelling languages used have to be described. These concepts are primarily meta-concepts, i.e. concepts which apply generally to any form of modelling activity.
21、It is not intended that these concepts will be formally defined, nor that they be used as the basis of formal definition of other concepts. 2 ITU-T Rec. X.902 (1995 E) ISO/IEC 10746-2 : 1996 (E) Any modelling activity identifies: a) elements of the universe of discourse; b) one or more pertinent lev
22、els of abstraction. The elements of the universe of discourse are entities and propositions. 6.1 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 modelling it is reserved to refer to things in the universe of dis
23、course being modelled. 6.2 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. 6.3 Abstraction: The process of suppressing irrelevant detail to establish a simplified model, or the result of t
24、hat process. 6.4 Atomicity: An entity is atomic at a given level of abstraction if it cannot be subdivided at that level of abstraction. Fixing a given level of abstraction may involve identifying which elements are atomic. 6.5 System: Something of interest as a whole or as comprised of parts. There
25、fore 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. NOTE - For modelling purposes, the concept of system is understood in its general, system-theoretic sense. The term “system” can refer to an information processi
26、ng system but can also be applied more generally. 6.6 Architecture (of a system): A set of rules to define the structure of a system and the interrelationships between its parts. 7 Basic linguistic concepts Whatever the concepts or semantics of a modelling language for the ODP Architecture, it will
27、be expressed in some syntax, which may include linear text or graphical conventions. It is assumed that any suitable language will have a grammar defining the valid set of symbols and well-formed linguistic constructs of the language. The following concepts provide a common framework for relating th
28、e syntax of any language used for the ODP Architecture to the interpretation concepts. 7.1 Term: A linguistic construct which may be used to refer to an entity. The reference may be to any kind of entity including a model of an entity or another linguistic construct. 7.2 Sentence: A linguistic const
29、ruct containing one or more terms and predicates; a sentence may be used to express a proposition about the entities to which the terms refer. A predicate in a sentence may be considered to refer to a relationship between the entities referred to by the terms linked. 8 Basic modelling concepts The d
30、etailed interpretation of the concepts defined in this clause will depend on the specification language concerned, but these general statements of concept are made in a language-independent way to allow the statements in different languages to be interrelated. The basic concepts are concerned with e
31、xistence and activity: the expression of what exists, where it is and what it does. 8.1 Object: A model of an entity. An object is characterized by its behaviour (see 8.6) and, dually, by its state (see 8.7). An object is distinct from any other object. An object is encapsulated, i.e. any change in
32、its state can only occur as a result of an internal action or as a result of an interaction (see 8.3) with its environment (see 8.2). An object interacts with its environment at its interaction points (see 8.11). Depending on the viewpoint, the emphasis may be placed on behaviour or on state. When t
33、he emphasis is placed on behaviour, an object is informally said to perform functions and offer services (an object which makes a function available is said to offer a service). For modelling purposes, these functions and services are specified in terms of the behaviour of the object and of its inte
34、rfaces (see 8.4). An object can perform more than one function. A function can be performed by the cooperation of several objects. ITU-T Rec. X.902 (1995 E) 3 ISO/IEC 10746-2 : 1996 (E) NOTES 1 The concepts of service and function are used informally to express the purpose of a piece of standardizat
35、ion. In the ODP family of standards, function and service are expressed formally in terms of the specification of the behaviour of objects and of the interfaces which they support. A “service” is a particular abstraction of behaviour expressing the guarantees offered by a service provider. 2 The exp
36、ression “use of a function” is a shorthand for the interaction with an object which performs the function. 8.2 Environment (of an object): The part of the model which is not part of that object. NOTE - In many specification languages, the environment can be considered to include at least one object
37、which is able to participate without constraint in all possible interactions (see 8.3) representing the process of observation. 8.3 Action: Something which happens. Every action of interest for modelling purposes is associated with at least one object. The set of actions associated with an object is
38、 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. NOTES 1 “Action” means “action occurrence”. Depending on context,
39、 a specification may express that an action has occurred, is occurring or may occur. 2 The granularity of actions is a design choice. An action need not be instantaneous. Actions may overlap in time. 3 Interactions may be labelled in terms of cause and effect relationships between the participating
40、objects. The concepts that support this are discussed in 13.3. 4 An object may interact with itself, in which case it is considered to play at least two roles in the interaction, and may be considered, in this context, as being a part of its own environment. 5 Involvement of the environment represen
41、ts observability. Thus, interactions are observable whereas internal actions are not observable, because of object encapsulation. 8.4 Interface: An abstraction of the behaviour of an object that consists of a subset of the interactions of that object together with a set of constraints on when they m
42、ay occur. Each interaction of an object belongs to a unique interface. Thus, the interfaces of an object form a partition of the interactions of that object. NOTES 1 An interface constitutes the part of an object behaviour that is obtained by considering only the interactions of that interface and b
43、y hiding all other interactions. Hiding interactions of other interfaces will generally introduce non-determinism as far as the interface being considered is concerned. 2 The phrase “an interface between objects” is used to refer to the binding (see 13.4.2) between interfaces of the objects concerne
44、d. 8.5 Activity: A single-headed directed acyclic graph of actions, where 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). 8.6 Behaviour (of an object): A collection of actions
45、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 sequentiality, non-determinism, concurrency or real-time constraints. A behaviour may include internal actions. The actions that
46、actually take place are restricted by the environment in which the object is placed. NOTES 1 The composition (see 9.1) of a collection of objects implicitly yields an equivalent object representing the composition. The behaviour of this object is often referred to simply as the behaviour of the coll
47、ection of objects. 2 Action and activity are degenerate cases of behaviour. 3 In general, several sequences of interactions are consistent with a given behaviour. 8.7 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 w
48、hich the object can take part. Since, in general, behaviour includes many possible series of actions in which the object might take part, knowledge of state does not necessarily allow the prediction of the sequence of actions which will actually occur. 4 ITU-T Rec. X.902 (1995 E) ISO/IEC 10746-2 : 1
49、996 (E) State changes are effected by actions; hence a state is partially determined by the previous actions in which the object took part. Since an object is encapsulated, its state cannot be changed directly from the environment, but only indirectly as a result of the interactions in which the object takes part. 8.8 Communication: The conveyance of information between two or more objects as a result of one or more interactions, possibly involving some intermediate objects. NOTES 1 Communications may be labelled in terms of a cause and effect relationship between the participating objects. C
