Network Working Group A. Pras
Request for Comments: 3444 University of Twente
Category: Informational J. Schoenwaelder
University of Osnabrueck
January 2003
Network Working Group A. Pras
Request for Comments: 3444 University of Twente
Category: Informational J. Schoenwaelder
University of Osnabrueck
January 2003
On the Difference between Information Models and Data Models
论信息模型与数据模型的区别
Status of this Memo
本备忘录的状况
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2003). All Rights Reserved.
版权所有（C）互联网协会（2003年）。版权所有。
Abstract
摘要
There has been ongoing confusion about the differences between Information Models and Data Models for defining managed objects in network management. This document explains the differences between these terms by analyzing how existing network management model specifications (from the IETF and other bodies such as the International Telecommunication Union (ITU) or the Distributed Management Task Force (DMTF)) fit into the universe of Information Models and Data Models.
关于在网络管理中定义托管对象的信息模型和数据模型之间的差异，人们一直存在困惑。本文件通过分析现有网络管理模型规范（来自IETF和国际电信联盟（ITU）或分布式管理工作组（DMTF）等其他机构）如何适应信息模型和数据模型的范围，解释了这些术语之间的差异。
This memo documents the main results of the 8th workshop of the Network Management Research Group (NMRG) of the Internet Research Task Force (IRTF) hosted by the University of Texas at Austin.
本备忘录是得克萨斯大学奥斯汀分校主办的互联网研究工作组网络管理研究组（NMRG）第八届研讨会的主要成果。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Information Models . . . . . . . . . . . . . . . . . . . . . . 3
4. Data Models . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
8. Informative References . . . . . . . . . . . . . . . . . . . . 7
9. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
10. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Information Models . . . . . . . . . . . . . . . . . . . . . . 3
4. Data Models . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
8. Informative References . . . . . . . . . . . . . . . . . . . . 7
9. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
10. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8
Currently multiple languages exist to define managed objects. Examples of such languages are the Structure of Management Information (SMI) [1], the Structure of Policy Provisioning Information (SPPI) [2] and, within the DMTF, the Managed Object Format (MOF) [3]. Despite the fact that multiple languages exist, a number of people still believe that none of these languages really suits all needs.
目前存在多种语言来定义托管对象。此类语言的示例包括管理信息结构（SMI）[1]、策略供应信息结构（SPPI）[2]，以及DMTF中的托管对象格式（MOF）[3]。尽管存在多种语言，但许多人仍然认为这些语言都不能满足所有的需要。
There have been many discussions to understand the advantages and disadvantages, as well as the main differences, between various languages. For instance, the IETF organized a BoF on "Network Information Modeling" (NIM) at its 48th meeting (Pittsburgh, August 2000). During these discussions, it turned out that people had a different understanding of the main terms, which caused confusion and long arguments. In particular, the meaning of the terms "Information Model" (IM) and "Data Model" (DM) turned out to be controversial.
为了理解各种语言之间的优缺点以及主要差异，已经进行了许多讨论。例如，IETF在其第48次会议（匹兹堡，2000年8月）上组织了一次关于“网络信息建模”（NIM）的BoF。在这些讨论中，人们对主要术语有不同的理解，这导致了混乱和长期争论。特别是，“信息模型”（IM）和“数据模型”（DM）这两个术语的含义引起了争议。
In an attempt to address this issue, the IRTF Network Management Research Group (NMRG) dedicated its 8th workshop (Austin, December 2000) to harmonizing the terminology used in information and data modeling. Attendees included experts from the IETF, DMTF and ITU, as well as academics who do research in this field (see the Acknowledgments section for a list of participants). The main outcome of this successful workshop -- a better understanding of the terms "Information Model" and "Data Model" -- is presented in this document.
为了解决这个问题，IRTF网络管理研究小组（NMRG）专门举办了第八次研讨会（奥斯汀，2000年12月），以协调信息和数据建模中使用的术语。与会者包括来自IETF、DMTF和ITU的专家，以及在该领域进行研究的学者（与会者名单见致谢部分）。本文档介绍了本次成功研讨会的主要成果——更好地理解“信息模型”和“数据模型”这两个术语。
Short definitions of these terms can also be found elsewhere (e.g., in RFC 3198 [8]). Compared to most other documents, this one explains the rationale behind the proposed definitions and provides examples.
这些术语的简短定义也可在其他地方找到（如RFC 3198[8]）。与大多数其他文件相比，本文件解释了拟议定义背后的基本原理，并提供了示例。
One of the key observations made at the NMRG workshop was that IMs and DMs are different because they serve different purposes.
NMRG研讨会上的一个关键观察结果是，IMs和DMs不同，因为它们的用途不同。
The main purpose of an IM is to model managed objects at a conceptual level, independent of any specific implementations or protocols used to transport the data. The degree of specificity (or detail) of the abstractions defined in the IM depends on the modeling needs of its designers. In order to make the overall design as clear as possible, an IM should hide all protocol and implementation details. Another important characteristic of an IM is that it defines relationships between managed objects.
IM的主要目的是在概念级别对托管对象进行建模，独立于用于传输数据的任何特定实现或协议。IM中定义的抽象的具体程度（或细节）取决于其设计者的建模需求。为了使总体设计尽可能清晰，IM应该隐藏所有协议和实现细节。IM的另一个重要特征是它定义了托管对象之间的关系。
DMs, conversely, are defined at a lower level of abstraction and include many details. They are intended for implementors and include protocol-specific constructs.
相反，DMs是在较低的抽象级别定义的，包含许多细节。它们是为实现者设计的，包括特定于协议的结构。
IM --> conceptual/abstract model
| for designers and operators
+----------+---------+
| | |
DM DM DM --> concrete/detailed model
for implementors
IM --> conceptual/abstract model
| for designers and operators
+----------+---------+
| | |
DM DM DM --> concrete/detailed model
for implementors
The relationship between an IM and DM is shown in the Figure above. Since conceptual models can be implemented in different ways, multiple DMs can be derived from a single IM.
IM和DM之间的关系如上图所示。由于概念模型可以以不同的方式实现，因此可以从单个IM派生多个DM。
Although IMs and DMs serve different purposes, it is not always possible to precisely define what kind of details should be expressed in an IM and which ones belong in a DM. There is a gray area where IMs and DMs overlap -- just like there are gray areas between the models produced during the analysis, high-level design and low-level design phases in object-oriented software engineering. In some cases, it is very difficult to determine whether an abstraction belongs to an IM or a DM.
尽管IMs和DMs有不同的用途，但并不总是能够精确地定义IM中应该表达什么样的细节，以及哪些细节属于DM。在IMs和DMs重叠的地方有一个灰色区域——就像在面向对象软件工程的分析、高级设计和低级设计阶段生成的模型之间有灰色区域一样。在某些情况下，很难确定抽象是属于IM还是DM。
IMs are primarily useful for designers to describe the managed environment, for operators to understand the modeled objects, and for implementors as a guide to the functionality that must be described and coded in the DMs. The terms "conceptual models" and "abstract models", which are often used in the literature, relate to IMs. IMs can be implemented in different ways and mapped on different protocols. They are protocol neutral.
IMs主要用于设计人员描述托管环境，操作员理解建模对象，实现人员作为DMs中必须描述和编码的功能指南。文献中经常使用的术语“概念模型”和“抽象模型”与国际监测系统有关。IMs可以以不同的方式实现，并映射到不同的协议上。它们是协议中立的。
An important characteristic of IMs is that they can (and generally should) specify relationships between objects. Organizations may use the contents of an IM to delimit the functionality that can be included in a DM.
IMs的一个重要特征是，它们可以（通常应该）指定对象之间的关系。组织可以使用IM的内容来界定DM中可以包含的功能。
IMs can be defined in an informal way, using natural languages such as English. An example of such an IM is provided by RFC 3290 [9], which describes a conceptual model of a Diffserv Router and specifies the relationships between the components of such a router that need to be managed. Within the IETF, however, it is exceptional that an IM be explicitly described, and even more that the IM and DM be specified in separate RFCs. In such cases, the document specifying the IM is usually an Informational RFC whereas the document defining the DM usually follows the Standards Track [4]. In general, most of
可以使用自然语言（如英语）以非正式的方式定义IMs。RFC 3290[9]提供了此类IM的一个示例，它描述了区分服务路由器的概念模型，并指定了需要管理的此类路由器组件之间的关系。然而，在IETF中，明确描述IM是例外，更重要的是在单独的RFC中指定IM和DM。在这种情况下，指定IM的文档通常是信息RFC，而定义DM的文档通常遵循标准轨道[4]。一般来说，大多数
the RFCs that define an SNMP Management Information Base (MIB) module also include some kind of informal description explaining parts of the model behind that MIB module. Such a model can be considered as a document of an IM. An example of this is RFC 2863, which defines "The Interfaces Group MIB" [10]. But most MIB modules published to date include only a rudimentary and incomplete description of the underlying IM.
定义SNMP管理信息库（MIB）模块的RFC还包括一些非正式的描述，解释MIB模块背后的部分模型。这样的模型可以被视为IM的文档。RFC 2863就是一个例子，它定义了“接口组MIB”[10]。但迄今为止发布的大多数MIB模块只包含对底层IM的基本和不完整的描述。
Alternatively, IMs can be defined using a formal language or a semi-formal structured language. One of the possibilities to formally specify IMs is to use class diagrams of the Unified Modeling Language (UML). Although such diagrams are still rarely used within the IETF, several other organizations routinely use them for defining IMs, including the DMTF, the ITU-T SG 4, 3GPP SA5, the TeleManagement Forum, and the ATM Forum. An important advantage of UML class diagrams is that they represent objects and the relationships between them in a standard graphical way. Because of this graphical representation, designers and operators may find it easier to understand the underlying management model. Although there are other techniques to graphically represent objects and relationships (e.g., Entity-Relationship (ER) diagrams), UML presents the advantage of being widely adopted in the industry and taught in universities. Also, many tools for editing UML diagrams are now available. UML is standardized by the Object Management Group (OMG) [5].
或者，可以使用正式语言或半正式结构化语言定义IMs。正式指定IMs的一种可能性是使用统一建模语言（UML）的类图。尽管此类图在IETF中仍然很少使用，但其他一些组织通常使用它们来定义IMs，包括DMTF、ITU-T SG 4、3GPP SA5、远程管理论坛和ATM论坛。UML类图的一个重要优点是，它们以标准的图形方式表示对象及其之间的关系。由于这种图形表示，设计者和操作员可能会发现更容易理解底层管理模型。尽管还有其他技术以图形方式表示对象和关系（例如，实体关系（ER）图），但UML具有在行业中被广泛采用和在大学教授的优势。此外，现在有许多用于编辑UML图的工具可用。UML由对象管理组（OMG）[5]标准化。
In general, it seems advisable to use object-oriented techniques to describe an IM. In particular, the notions of abstraction and encapsulation, as well as the possibility that object definitions include methods, are considered to be important.
一般来说，使用面向对象技术来描述IM似乎是明智的。特别是，抽象和封装的概念以及对象定义包含方法的可能性被认为是重要的。
Compared to IMs, DMs define managed objects at a lower level of abstraction. They include implementation- and protocol-specific details, e.g. rules that explain how to map managed objects onto lower-level protocol constructs.
与IMs相比，DMs在较低的抽象级别上定义托管对象。它们包括特定于实现和协议的详细信息，例如解释如何将托管对象映射到较低级别的协议构造的规则。
Most of the management models standardized to date are DMs. Examples include:
迄今为止，大多数标准化的管理模式都是DMs。例子包括：
o Management Information Base (MIB) modules defined within the IETF. The language (syntax) used to define these DMs is called the "Structure of Management Information" (SMI) [1] and is derived from ASN.1 [6].
o IETF中定义的管理信息库（MIB）模块。用于定义这些DMs的语言（语法）称为“管理信息结构”（SMI）[1]，源自ASN.1[6]。
o Policy Information Base (PIB) modules, developed within the IETF. Their syntax is defined by the "Structure of Policy Provisioning Information" (SPPI) [2], which is close to SMI and is also derived from ASN.1 [6].
o 在IETF中开发的政策信息库（PIB）模块。它们的语法由“策略供应信息结构”（SPPI）[2]定义，该结构接近SMI，也源自ASN.1[6]。
o Management Information Base (MIB) modules, originally defined by the ISO and currently maintained and enhanced by the ITU-T. The syntax of these DMs is specified in the "Guidelines for the Definition of Managed Objects" (GDMO) [7]. GDMO MIB modules make use of object-oriented principles.
o 管理信息库（MIB）模块，最初由ISO定义，目前由ITU-T维护和增强。这些DMs的语法在“管理对象定义指南”（GDMO）[7]中规定。GDMO MIB模块使用面向对象的原则。
o CIM Schemas, developed within the DMTF. The DMTF publishes them in two forms: graphical and textual. The graphical forms use UML diagrams and are not normative (because not all details can be represented graphically). They can be downloaded from the DMTF Web site in PDF and Visio formats. (Visio is a tool to draw UML class diagrams.) The textual forms are normative and written in a language called the "Managed Object Format" (MOF) [3]. CIM Schemas are object-oriented.
o CIM模式，在DMTF中开发。DMTF以两种形式发布它们：图形和文本。图形形式使用UML图，不规范（因为并非所有细节都可以用图形表示）。可以从DMTF网站下载PDF和Visio格式。（Visio是一种绘制UML类图的工具。）文本形式是规范的，并用一种称为“托管对象格式”（MOF）的语言编写[3]。CIM模式是面向对象的。
Because CIM Schemas support a graphical notation whereas IETF MIB modules do not, designers and operators may find it easier to understand CIM Schemas than IETF MIB modules. One could therefore argue that CIM Schemas are closer to IMs than IETF MIB modules.
由于CIM模式支持图形表示法，而IETF MIB模块不支持图形表示法，因此设计人员和操作员可能会发现理解CIM模式比理解IETF MIB模块更容易。因此，有人可能认为CIM模式比IETF MIB模块更接近IMs。
The Figure below summarizes these examples. The languages that are used to define the DMs are shown between brackets.
下图总结了这些示例。用于定义DMs的语言显示在括号之间。
IM --> IM
|
+----------+-------+-------+--------------+
| | | |
MIB PIB CIM schema OSI-MIB --> DM
(SMI) (SPPI) (MOF) (GDMO)
IM --> IM
|
+----------+-------+-------+--------------+
| | | |
MIB PIB CIM schema OSI-MIB --> DM
(SMI) (SPPI) (MOF) (GDMO)
To illustrate what details are included in a DM, let us consider the example of IETF MIB modules. As opposed to IMs, IETF MIB modules include details such as OID assignments and indexing structures. The relationships defined in the IM are implemented as OID pointers or realized through indexing relationships specified in INDEX clauses. Many other implementation-specific details are included, such as MAX-ACCESS and STATUS clauses and conformance statements.
为了说明DM中包含哪些细节，让我们考虑IETF MIB模块的例子。与IMs相反，IETF MIB模块包括OID分配和索引结构等细节。IM中定义的关系作为OID指针实现，或通过索引子句中指定的索引关系实现。还包括许多其他特定于实现的细节，如MAX-ACCESS和STATUS子句以及一致性声明。
A special kind of DM language is the SMIng language defined by the NMRG. This language was designed at a higher conceptual level than SMIv1/SMIv2 and SPPI. In fact, one of the intentions behind SMIng was to stop the proliferation of different DM languages within the IETF and to harmonize the various models. As a result, MIB and PIB
一种特殊的DM语言是NMRG定义的SMIng语言。这种语言是在比SMIv1/SMIv2和SPPI更高的概念层次上设计的。事实上，SMIng背后的意图之一是阻止IETF中不同DM语言的扩散，并协调各种模型。因此，MIB和PIB
modules defined in SMIng can be mapped on different underlying protocols. There is a mapping on SNMP and another mapping on COPS-PR. SMIng is therefore more protocol neutral than other IETF approaches. It also supports some object-oriented principles and provides extension mechanisms that allow the addition of new features (e.g., the support for methods). New features can then be used when they are supported by the underlying protocols, without breaking SMIng implementations. Still, SMIng should be considered a DM. For instance, to express relationships between managed objects, techniques such as UML and ER diagrams still give better results because these diagrams are easier to understand.
SMIng中定义的模块可以映射到不同的底层协议。SNMP上有一个映射，COPS-PR上有另一个映射。因此，SMIng比其他IETF方法更具协议中立性。它还支持一些面向对象的原则，并提供允许添加新特性（例如，对方法的支持）的扩展机制。当底层协议支持新功能时，就可以使用它们，而不会破坏SMIng实现。不过，SMIng应该被视为DM。例如，为了表示托管对象之间的关系，UML和ER图等技术仍然可以提供更好的结果，因为这些图更容易理解。
Note that the IETF SMING Working Group took a different approach and decided not to use the SMIng language defined by the NMRG. Instead, the SMING Working Group is developing a third version of SMI (SMIv3) that is primarily targeted towards SNMP, and which incorporates only some of the ideas developed within the NMRG.
请注意，IETF SMING工作组采取了不同的方法，并决定不使用NMRG定义的SMING语言。相反，SMIN工作组正在开发SMI（SMIv3）的第三个版本，该版本主要针对SNMP，并且只包含NMRG中开发的一些思想。
The meaning of the terms Information Model and Data Model has no direct security impact on the Internet.
术语信息模型和数据模型的含义对互联网没有直接的安全影响。
The authors would like to thank everyone who participated in the 8th NMRG workshop (in alphabetic order): Szabolcs Boros, Marcus Brunner, David Durham, Dave Harrington, Jean-Philippe Martin-Flatin, George Pavlou, Robert Parhonyi, David Perkins, David Sidor, Andrea Westerinen and Bert Wijnen.
作者要感谢参加第八届NMRG研讨会的所有人（按字母顺序排列）：Szabolcs Boros、Marcus Brunner、David Durham、Dave Harrington、Jean-Philippe Martin Flatin、George Pavlou、Robert Parhonyi、David Perkins、David Sidor、Andrea Westerinen和Bert Wijnen。
[1] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[1] McCloghrie，K.，Perkins，D.和J.Schoenwaeld，“管理信息的结构版本2（SMIv2）”，STD 58，RFC 2578，1999年4月。
[2] McCloghrie, K., Fine, M., Seligson, J., Chan, K., Hahn, S., Sahita, R., Smith, A. and F. Reichmeyer, "Structure of Policy Provisioning Information (SPPI)", RFC 3159, August 2001.
[2] McCloghrie，K.，Fine，M.，Seligson，J.，Chan，K.，Hahn，S.，Sahita，R.，Smith，A.和F.Reichmeyer，“策略供应信息的结构（SPPI）”，RFC 3159，2001年8月。
[3] Distributed Management Task Force, "Common Information Model (CIM) Specification Version 2.2", DSP 0004, June 1999.
[3] 分布式管理任务组，“公共信息模型（CIM）规范版本2.2”，DSP 0004，1999年6月。
[4] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996.
[4] Bradner，S.，“互联网标准过程——第3版”，BCP 9，RFC 2026，1996年10月。
[5] Object Management Group, "Unified Modeling Language (UML), Version 1.4", formal/2001-09-67, September 2001.
[5] 对象管理组，“统一建模语言（UML），1.4版”，formal/2001-09-672001年9月。
[6] International Organization for Standardization, "Information processing systems - Open Systems Interconnection - Specification of Abstract Syntax Notation One (ASN.1)", International Standard 8824, December 1987.
[6] 国际标准化组织，“信息处理系统-开放系统互连-抽象语法符号1规范（ASN.1）”，国际标准88241987年12月。
[7] International Telecommunication Union, "Information technology - Open Systems Interconnection - Structure of Management Information: Guidelines for the Definition of Managed Objects", Recommendation X.722, 1992.
[7] 国际电信联盟，“信息技术-开放系统互连-管理信息结构：管理对象定义指南”，建议X.7221992。
[8] Westerinen, A., Schnizlein, J., Strassner, J., Scherling, M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry, J. and S. Waldbusser, "Terminology for Policy-Based Management", RFC 3198, November 2001.
[8] 威斯特林，A.，施尼兹林，J.，斯特拉斯纳，J.，舍林，M.，奎因，B.，赫尔佐格，S.，休恩，A.，卡尔森，M.，佩里，J.和S.瓦尔德布瑟，“基于政策的管理术语”，RFC 3198，2001年11月。
[9] Bernet, Y., Blake, S., Grossman, D. and A. Smith, "An Informal Management Model for Diffserv Routers", RFC 3290, May 2002.
[9] Bernet，Y.，Blake，S.，Grossman，D.和A.Smith，“区分服务路由器的非正式管理模型”，RFC 3290，2002年5月。
[10] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, June 2000.
[10] McCloghrie，K.和F.Kastenholz，“接口组MIB”，RFC 28632000年6月。
Aiko Pras University of Twente PO Box 217 7500 AE Enschede The Netherlands
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