Network Working Group A. Westerinen
Internet-Draft C. Elliott
Expires: November 12, 2001 Cisco Systems
J. Schoenwaelder
F. Strauss
TU Braunschweig
J. Jason
Intel Corporation
W. Weiss
Ellacoya Networks
May 14, 2001
SMIng Requirements
draft-ietf-sming-reqs-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document describes the requirements of a data modeling language
suitable for the modeling of network management constructs, and which
can be translated into the various other standardized representations
that we have today - at a minimum, at a minimum SMIv2 MIBs and SPPI
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PIBs. This document will describe requirements for the construction
of a modeling language and the representation of basic modeling
constructs. These requirements are generally described in the areas
of reusability, extensibility, associability, naming, expressiveness
of data definitions through constraints, and inheritance. The
purpose of this document is to ensure that subsequent documents that
describe the conventions for the language are complete and consistent
with the requirements stated herein.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Specific Requirements for SMIng . . . . . . . . . . . . . . 5
3.1 Textual Representation . . . . . . . . . . . . . . . . . . . 6
3.2 Human Readability . . . . . . . . . . . . . . . . . . . . . 6
3.3 Machine Readability . . . . . . . . . . . . . . . . . . . . 7
3.4 Naming . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.5 Namespace Control . . . . . . . . . . . . . . . . . . . . . 8
3.6 Modules . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.7 Protocol Independence . . . . . . . . . . . . . . . . . . . 8
3.8 Protocol Mapping . . . . . . . . . . . . . . . . . . . . . . 8
3.9 Translation to Other Data Definition Languages . . . . . . . 8
3.10 Incomplete Translations . . . . . . . . . . . . . . . . . . 9
3.11 Instance Naming . . . . . . . . . . . . . . . . . . . . . . 9
3.12 Base Data Types . . . . . . . . . . . . . . . . . . . . . . 9
3.13 Extended Data Types . . . . . . . . . . . . . . . . . . . . 9
3.14 Instance Pointers . . . . . . . . . . . . . . . . . . . . . 9
3.15 Row Pointers . . . . . . . . . . . . . . . . . . . . . . . . 10
3.16 Base Type Set . . . . . . . . . . . . . . . . . . . . . . . 10
3.17 Accessibility . . . . . . . . . . . . . . . . . . . . . . . 11
3.18 Derived Types . . . . . . . . . . . . . . . . . . . . . . . 12
3.19 Enumerations . . . . . . . . . . . . . . . . . . . . . . . . 12
3.20 Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.21 Creation/Deletion . . . . . . . . . . . . . . . . . . . . . 12
3.22 Range and Size Constraints . . . . . . . . . . . . . . . . . 13
3.23 Constraints on Pointers . . . . . . . . . . . . . . . . . . 13
3.24 Uniqueness . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.25 Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.26 Table Existence Relationships . . . . . . . . . . . . . . . 14
3.27 Extension Rules . . . . . . . . . . . . . . . . . . . . . . 14
3.28 Categories . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.29 Agent Capabilities . . . . . . . . . . . . . . . . . . . . . 15
3.30 Remove IMPLIED Keyword . . . . . . . . . . . . . . . . . . . 15
3.31 No Redundancy . . . . . . . . . . . . . . . . . . . . . . . 15
3.32 Discriminated Unions . . . . . . . . . . . . . . . . . . . . 15
3.33 Classes . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.34 Single Inheritance . . . . . . . . . . . . . . . . . . . . . 16
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3.35 Abstract vs. Concrete Classes . . . . . . . . . . . . . . . 17
3.36 Relationships . . . . . . . . . . . . . . . . . . . . . . . 18
3.37 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.38 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.39 Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.40 Composition . . . . . . . . . . . . . . . . . . . . . . . . 20
3.41 Existence Constraints . . . . . . . . . . . . . . . . . . . 20
3.42 Ordering Constraints . . . . . . . . . . . . . . . . . . . . 21
3.43 Attribute Transaction Constraints . . . . . . . . . . . . . 21
3.44 Attribute Value Constraints . . . . . . . . . . . . . . . . 21
3.45 Associations . . . . . . . . . . . . . . . . . . . . . . . . 22
3.46 Association Cardinalities . . . . . . . . . . . . . . . . . 22
3.47 Method Constraints . . . . . . . . . . . . . . . . . . . . . 22
3.48 Table Relationships . . . . . . . . . . . . . . . . . . . . 23
3.49 Float Data Types . . . . . . . . . . . . . . . . . . . . . . 23
3.50 Compliance and Conformance . . . . . . . . . . . . . . . . . 23
3.51 Categories of Modules . . . . . . . . . . . . . . . . . . . 23
3.52 Language Extensibility . . . . . . . . . . . . . . . . . . . 24
3.53 Length of Identifiers . . . . . . . . . . . . . . . . . . . 24
3.54 Why Are So Many SMIv1/v2 So Error Tolerant? . . . . . . . . 24
3.55 Core Language Keywords vs. Defined Identifiers . . . . . . . 25
3.56 i18n . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.57 Special Characters in Texts . . . . . . . . . . . . . . . . 26
3.58 Mapping Modules to Files . . . . . . . . . . . . . . . . . . 26
3.59 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.60 Simple Grammar . . . . . . . . . . . . . . . . . . . . . . . 27
3.61 Place of Module Information . . . . . . . . . . . . . . . . 27
3.62 Fully Qualified Identifiers . . . . . . . . . . . . . . . . 28
3.63 Readable Revision Date Representation . . . . . . . . . . . 28
3.64 Make Status Information Optional . . . . . . . . . . . . . . 28
3.65 Units and Default Values of Defined Types . . . . . . . . . 29
3.66 Arbitrary Unambiguous Identities . . . . . . . . . . . . . . 30
3.67 Remove OIDs from the Core Language . . . . . . . . . . . . . 30
3.68 Module Namespace . . . . . . . . . . . . . . . . . . . . . . 30
3.69 Problem: Where to Put Constraints Required by the Protocol? 31
3.70 Problem: Phrasing Descriptions . . . . . . . . . . . . . . . 31
3.71 Problem: Mapping Protocol Specific Attributes . . . . . . . 32
3.72 Hyphens in Identifiers . . . . . . . . . . . . . . . . . . . 32
3.73 The Set of Spec Documents . . . . . . . . . . . . . . . . . 33
3.74 Allow Refinement of All Definitions in Conformance Statements 33
3.75 Referencing a Group of Instances of a Class . . . . . . . . 33
4. Conformance and Capability Reporting . . . . . . . . . . . . 34
5. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . 34
6. Security Considerations . . . . . . . . . . . . . . . . . . 35
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35
References . . . . . . . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 36
Full Copyright Statement . . . . . . . . . . . . . . . . . . 38
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1. Introduction
This document describes the requirements for the definition of a new
object-oriented, data modeling language that is mappable to SMIv2
[2], [3], [4] MIBs and [8] PIBs. Concepts such as classes,
attributes, methods, conventions for organization into reusable data
structures, and mechanisms for representing relationships are
discussed.
Conventions used in this document:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [1].
2. Motivation
As networking technology has evolved, a diverse set of technologies
has been deployed to manage the resulting products. These vary from
Web based products, to standard management protocols and text
scripts. The underlying systems to be manipulated are represented in
varying ways including implicitly in the system programming, via
proprietary data descriptions, or with standardized descriptions
using a range of technologies including MIBs [5], PIBs [9], or LDAP
[6] schemas. The result is that network applications and services
such as DHCP or Differentiated Services may be represented in many
different inconsistent fashions. SMIng is proposed as a new modeling
language to align the languages defined in the SMIv2 and SPPI
documents (the languages for writing MIBs and PIBs), since these are
very similar. Therefore, SMIng language constructs SHOULD be
mappable to MIBs and PIBs, but also be protocol independent and allow
mappings to other definitional languages (such as LDAP schemas). The
word, SHOULD, is used in the paragraph above since another motivation
for SMIng is to permit a more expressive and complete representation
of the modeled information. This implies that all information
expressed in SMIng may not be directly mappable to a MIB or PIB
construct, but may have to be conveyed in documentation or via other
mechanisms. Examples of additional expressiveness and completeness
are the ability to define relationships between objects, the
expression of constraints on objects and properties, and the ability
to define methods. This issue is more fully discussed in Section
3.37 and others, below.
3. Specific Requirements for SMIng
The following sections define the requirements for the definition of
an object-oriented, data-modeling language. Frank Strauss also
maintains a web page[10] that contains the same information, albeit
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in a slightly different format. Each requirement has the following
information:
o Status: a field with one or more of the following values:
* basic: considered a basic requirement for SMIng and is
contained in SMIv2 and/or SPPI.
* align: supported in different ways in SMIv2 and SPPI and they
must be aligned.
* must: considered a fix for a proven problem in SMIv2 and/or
SPPI.
* should: modifies something that is often misused, or would be
nice to have if it can be easily done and does not cause
additional complexity or delay.
* new: considered a new feature which is not required in SMIng,
but could be added if working group consensus to do so is
reached.
o From: a field which defines where the requirement was derived from
and has one or more of the following values:
* WG: has been proposed during working group discussions.
* SMI: exists already in SMIv2.
* SPPI: exists already in SPPI.
* SMIng: exists in current SMIng specification proposal, but not
in SMIv2 or SPPI.
* Charter: exists in working group charter.
* Individual: proposed by working group participant.
o Description: a quick description of the requirment.
o Motivation: rationale for the requirement
o Discussion: discussion generated by the requirement
3.1 Textual Representation
Status: basic
From: SMI, SPPI, WG
Description: SMIng definitions must be represented in a textual
format.
Motivation: General IETF consensus.
3.2 Human Readability
Status: basic
From: WG
Description: The syntax should make it possible for humans to read
and write SMIng modules. It should be possible to read and write
SMIng modules with text processing tools.
Motivation: The syntax should make it easy for humans to read and
write SMIng modules.
Discussion:
* Jamie: One thing I have noticed reading the IPsec PIB and MIB
documents is that the semantics of the model being presented
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are easily lost. The reason this is important to me is as a
co-author on the IPsec policy model, I want to make sure that
the PIB and MIB are semantically equivalent to the policy model
so that they represent the same information. Parsing through
the SMI and SPPI to understand the semantics of the particular
derivation for me is excruciatingly painful. I think that a
language that is more akin to C would make that human parsing
of the PIB/MIB much easier. As it stands now, I am relegated
to drawing pictures of the tables in order to understand what
is going on.
* Todd A Anderson: I would highly prefer a C-like syntax (or a
CORBA IDL-like syntax given than CORBA IDL is similar to C-like
syntax) to an ANS1-like syntax. I think that C-like syntax is
clearer and more straight-forward.
* David Putzolu in consequence of his comments on #37 and #45-46:
Finally, if I were brave enough to try to satisfy the above
mentioned requirements in SMIng, doing so and expressing the
relevant syntax in ASN.1 sounds extremely painful - if we must
go down this path, lets do it using something C++, or Java-like
- that would at least give a syntactic foundation that is
relevant to writing a programming language.
3.3 Machine Readability
Status: basic
From: SMI, SPPI
Description: The syntax should make it easy to implement parsers. A
complete ABNF specification of the grammar is desirable.
Furthermore, the language should forbid things like forward
references unless they are unavoidable.
Motivation: A complete specification of the language grammar in ABNF
encourages the usage of compiler toolkits to construct solid
parsers. Avoiding unnecessary forward references simplifies
parser internal data management and allows for early error
detection.
3.4 Naming
Status: basic
From: SMI, SPPI
Description: SMIng should provide mechanisms to uniquely identify
attributes, groups of attributes, and events. It is necessary to
specify how name collisions are handled.
Motivation: Need to unambiguously identify definitions of various
kinds. Some SMI implementations have problems with different
objects from multiple modules but with the same name.
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3.5 Namespace Control
Status: basic
From: SMI, SPPI
Description: There should be a centrally controlled namespace for
standard named items. A distributed namespace should be supported
to allow vendor-specific naming.
Motivation:
3.6 Modules
Status: basic
From: SMI, SPPI
Description: SMIng must provide a mechanism for uniquely identifying
a module, and specifying the status of a module, the contact
person for a module, the revision information for a module, and
the purpose of a module.
Motivation: SMIng must provide mechanisms to group definitions into
modules and it must provide rules to reference definitions from
other modules
SMIng must provide mechanisms to detail the minimum requirements
implementors must meet to claim conformance to a standard based on
the module.
Modularity, namespace scoping, and independent advancement of
documents.
3.7 Protocol Independence
Status: basic
From: Charter
Description: SMIng must define protocol independent data definitions.
Motivation: So they can be used with multiple protocols.
3.8 Protocol Mapping
Status: basic
From: Charter
Description: SMIng MUST define mappings of protocol independent data
definitions to the SNMP and COPS-PR protocols.
Motivation: SMIng working group charter.
3.9 Translation to Other Data Definition Languages
Status: basic
From: Charter
Description: SMIng language constructs SHOULD be mappable to MIBs and
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PIBs and allow mappings to other definitional languages (such as
LDAP schemas).
Motivation: Backwards compatibility with existing tools.
3.10 Incomplete Translations
Status: basic
From: WG
Description: Reality sucks. All information expressed in SMIng may
not be directly translatable to a MIB or PIB construct, but all
information should be able to be conveyed in documentation or via
other mechanisms.
Motivation: SMIng working group requires this to ease transition.
3.11 Instance Naming
Status: align
From: SMI, SPPI
Description: Instance naming is subject of the protocol mappings and
not part of the protocol neutral model. INDEX, PIB-INDEX must be
accommodated.
Motivation: COPS-PR and SNMP have different instance identification
schemes that must be aligned in the protocol specific mappings.
3.12 Base Data Types
Status: basic
From: SMI, SPPI
Description: SMIng must support the base data types Integer32,
Unsigned32, Integer64, Unsigned64, Enumeration, Bits, OctetString.
Motivation: Most are already common. Unisgned64 and Integer64 are in
SPPI, must fix in SMI.
3.13 Extended Data Types
Status: align
From: SMI, SPPI
Description: SMIng must allow a mechanism to allow types to be
defined as new types which provide additional semantics.
Counters, Gauges, Strings, etc.
Motivation: SMI uses application types and textual conventions. SPPI
uses derived types.
3.14 Instance Pointers
Status: basic
From: SPPI
Description: SMIng must allow specifying pointers to instances.
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Motivation: It is common practice in MIBs and PIBs to point to other
instances.
Discussion:
* Jamie: It is common when data modeling to reference another
object instead of embedding the referenced object inside of the
object doing the referencing. This is also important as it
allows objects to have independent lifetimes as well as be
referenced by many objects.
* Jamie: Can someone please elaborate on the differences between
#14 (Instance Pointers) and #15 (Row Pointers). Can they be
thought of in this way? Instance pointers are typed pointers,
whereas row pointers are void pointers. With the distinction
being that an instance pointer may only reference a row in one
type of table, while a row pointer may reference a row in any
kind of table?
* Juergen: I think the terms are used as defined in RFC 2579
(InstancePointer and RowPointer). The RowPointer always points
to an instance of a row while the InstancePointer can also
point to a particular cell in a table. Note that this has
nothing to do with a typed pointer (a concept which does not
really exist in SMIv2). SPPI however has ways to type pointers
- that is to restrict them so that they can not point to
everything.
(Using a class-based terminology, the difference is whether we
are done with supporting pointers to class instances or whether
we also need pointers to concrete attributes of class
instances.)
3.15 Row Pointers
Status: align
From: SMI, SPPI
Description: SMIng must allow specifying pointers to rows.
Motivation: It is common practice in MIBs and PIBs to point to other
rows (see RowPointer, PIB-REFERENCES).
3.16 Base Type Set
Status: basic
From: SMI, SPPI
Description: SMIng must support a fixed set of base types of fixed
size and precision. The list of base types should not be
extensible.
Motivation: Interoperability.
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3.17 Accessibility
Status: align
From: SMI, SPPI
Description: Attribute definitions must indicate whether attributes
can be read, written, created, deleted, and whether they are
accessible for notifications, or are non- accessible. Align PIB-
ACCESS and MAX-ACCESS, and PIB-MIN-ACCESS and MIN-ACCESS.
Motivation: Interoperability.
Discussion:
* Frank: To some degree accessibility might depend on the
protocol. Creation/deletion information might be protocol
dependent(?). `Accessible for notify' might be protocol
dependent(?). Do we need `write-only'?
* Robert Story: There is a recent thread over in the SNMPv3 list
in this vein. Someone asked what they should return for a set-
able password object: asterisks, empty string, NULL, etc. A
syntax of write-only would help in this case.
* David H.: Row creation/deletion is a fundamental feature of
SMIv2 and is required for backward compatibility and
interoperability. Accessible-for-notify is a feature of SMIv2
and must be supported for backwards compatibility and
interoperability.
* David Perkins: Row creation/deletion is not really part of the
SMI except for the status of read-create. Otherwise, the SMI
is blissfully ignorant of creation and deletion. You may claim
that the RowStatus TC makes creation and deletion part a
fundamental feature. If so, I disagree, since the SMI does not
require one to use the RowStatus TC for creation/deletion and
when RowStatus is used, there is nothing special about the
table and columns that use it.
* David Perkins: On status accessible-for-notify, this is a
status value whose usage and interpretation has been twisted
since its creation and is abused in almost every case where it
is used. It increases the difficulty of testing, and can
easily result in errors that show up only during exceptional
situations.
* Frank: Let's be precise: Not creation/deletion is a feature of
SMIv2, but a notation that allows to express whether a table
allows creation/deletion of instances through protocol
operations. I agree that both, create/delete information and
accessible-for-notify information, is required in SMIng, but
I'm not sure whether we need it in the protocol neutral or in
the protocol dependant parts.
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3.18 Derived Types
Status: basic
From: SMI, SPPI
Description: SMIng must allow a mechanism to allow base types to be
defined as new types which provide additional semantics. It may
be desirable to also allow the derivation of new types from
derived types.
Motivation: Textual Conventions permit this in SMIv2. Derived types
permit this in SPPI.
3.19 Enumerations
Status: basic
From: SMI, SPPI
Description: SMIng should provide support for enumerations with a
distributed and a centrally controlled namespace.
Motivation: SMIv2 already has enumerated numbers and OIDs that can be
used to identify things. Enumerated numbers are defined in a
single place while OIDs can be defined independently in arbitrary
places.
3.20 Events
Status: basic
From: SMI, SPPI
Description: SMIng must provide mechanisms to define events which
identify significant state changes.
Motivation: These represent the protocol- independent events that
lead to SMI notifications or SPPI reports.
3.21 Creation/Deletion
Status: basic
From: SMI, SPPI
Description: SMIng should support a mechanism to define
creation/deletion operations for instances. Specific
creation/deletion errors, such as INSTALL-ERRORS, must be
supported.
Motivation: Available for row creation in SMI, and available in SPPI.
Discussion:
* Frank: Let's not mix up protocol operations and the data model.
SMI does not have what this issue demands and IMHO this issue's
status should be `new' instead of `basic'.
* David H.: draft-ietf-rap-sppi-06.txt has Install-ERRORS as part
of the SPPI grammar. Both SMI and SPPI discuss "read-create".
rfc2578.txt discusses using the MAX-ACCESS clause to indicate
whether it makes protocol sense to create an instance of an
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object. As I see it, both recognize the need to be able to
create "things" in the protocol. RFC2579 has the RowStatus T-C
which explicitly discusses how to delete a "thing" in the
protocol. SPPI, in the description of the ReferenceID,
explicitly discusses deleting an instance of a PRI. All of
these discussions of creation/deletion are found in the
SMI/SPPI documents, not in the SNMP or COPS/PR protocol
documents.
* Frank: Ok. So the first sentence of this requirement's
description should be reworded to something like: SMIng should
support a mechanism to define whether creation/deletion
protocol operations for instances would make sense. This is
already covered by issue #17.
3.22 Range and Size Constraints
Status: basic
From: SMI, SPPI
Description: SMIng must allow specifying range and size constraints
where applicable.
Motivation: The SMI and SPPI both support range and size constraints.
3.23 Constraints on Pointers
Status: basic
From: SPPI
Description: SMIng must allow specifying the types of objects to
which a pointer may point.
Motivation: Allows code generators to detect and reject illegal
pointers automatically. Can also be used to automatically
generate more reasonable implementation-specific data structures.
3.24 Uniqueness
Status: basic
From: SPPI
Description: SMIng should allow to specify uniqueness constraints on
attributes.
Motivation: Knowledge of the uniqueness constraints on attributes
allows to verify protocol specific mappings (e.g. INDEX clauses).
The knowledge can also be used by code generators to improve
generated implementation-specific data structures.
3.25 Tables
Status: basic
From: SMI, SPPI
Description: SMIng should provide a mechanism for grouping attributes
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as tables.
Motivation:
3.26 Table Existence Relationships
Status: basic
From: SMI, SPPI
Description: SMIng should support INDEX, AUGMENTS, and EXTENDS.
Motivation: These three table existence relationships exists either
in the SMIv2 or the SPPI.
3.27 Extension Rules
Status: basic
From: SMI
Description: SMIng must provide clear rules how one can extend SMIng
modules without causing interoperability problems "over the wire".
Motivation: SMIv2 and SPPI have extension rules.
3.28 Categories
Status: basic
From: SPPI
Description: SMIng must provide mechanisms group definitions into
subject categories. Concrete instances may only exist in the
scope of a given subject category or context.
Motivation: To scope the categories to which a module applies. In
SPPI this is used to allow a division of labor between multiple
client types.
Discussion:
* Jamie: Is this akin to C++ namespaces (apologies to those who
are not familiar with them) in that they allow for scoping in
order to reduce/prevent name collisions? Or, is this the
purpose of #68 (Module Namespace)? If #68 serves this purpose,
I would like some more clarification on #28 so that I can get
them straight in my mind.
* Juergen: This #28 is not about C++ namespacese. Categories are
a way to categorize definitions - e.g. all the definitions
relevant for a diffserv manager or all the definitions relevant
for the security manager. COPS/PR and SPPI have this concept.
The SNMP world sometimes uses contexts to achieve something
similar. I once had a long debate with Keith about the
difference between contexts and subject categories and I am
still confused about it. ;-)
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3.29 Agent Capabilities
Status: basic
From: SMI
Description: SMIng must provide mechanisms to describe
implementation.
Motivation: To permit manager to determine variations from the
standard for an implementation.
Discussion:
* Frank: Capability statements in MIB modules are hardly useful
to managers, since in most cases they are simply not available.
Agent capabilities should be retrievable at runtime from the
agent itself through something like a capabilities MIB. Hence,
I suggest to drop `agent capabilities' from the core SMIng
language.
* Jamie: I would like to second the idea that #29 (Agent
Capabilities) be removed from the SMIng requirements. This
does not seem to belong at this level.
3.30 Remove IMPLIED Keyword
Status: should
From: SMI
Description: SMIng SNMP mapping should remove the IMPLIED indexing
schema.
Motivation: It is impossible to extend tables which contain IMPLIED
indexes without causing the extended table being in a different
lexicographic order.
Discussion:
* Frank: The SNMP mapping must keep IMPLIED for compatibility.
But it should be clearly stated that it must not be used in
newly defined SNMP mappings.
3.31 No Redundancy
Status: should
From: SMI
Description: The SMIng language should avoid redundancy.
Motivation: Remove any textual redundancy for things like table
entries and SEQUENCE definitions, which only increase
specifications without providing any value.
3.32 Discriminated Unions
Status: should
From: WG
Description: SMIng should support a standard format for discriminated
unions.
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Motivation: Allows to group related attributes together, such as
InetAddressType (discriminator) and InetAddress, InetAddressIPv4,
InetAddressIPv6 (union). The lack of discriminated unions has
also lead to relatively complex sparse table work-arounds in some
DISMAN mid-level manager MIBs.
3.33 Classes
Status: new
From: SMIng
Description: SMIng should provide a mechanism for reuse of non-
divisible, extensible attribute groupings.
Motivation: Required to map the same grouping of attributes into SNMP
and COPS-PR tables. Allows to do index reordering without having
to redefine the grouping of attributes. Allows to group related
attributes together (InetAddressType, InetAddress).
Discussion:
* Jamie: I agree with the motivation - I think it is a good thing
to be able to group attributes together for reuse. However, I
am wondering if the name classes can be changed to something
more generic. I don't know if "structures" are any better, but
I would like to see a different description.
* Jamie later on: Would it be possible to name #33 (Classes) to
something like "Attribute Groups"?
* Juergen: Fine with me.
* David Putzolu: Methods are strongly associated with classes in
the programming language lexicon, so choosing a different name
is a good idea.
* David D.: How about Attribute Class or aclass for short? Given
your comment to #34 below, I think the word "class" implies
inheritance abilities, whereas Attribute Groups, Structures,
etc. do not.
3.34 Single Inheritance
Status: new
From: SMIng
Description: SMIng should provide support for mechanisms to extend
attribute groupings (inheritance).
Motivation: Allows to extend grouping of attributes, like a generic
DiffServ scheduler, with attributes for a specific scheduler,
without cut&paste.
Discussion:
* Frank: I strongly suggest to decide whether this is a
requirement after a few examples are found including their
mappings to SNMP and COPS-PR tables! If we look at the example
above, each inherited scheduler would have to remain a
scheduler whose instances all appear in a common scheduler
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table. Thus the mapping to SNMP should lead to a basic table
that holds all common attributes (the parent class?) and a
number of table augmentations. Currently, I see now way how
inheritence could help in this situation. Cut&paste is not
needed. Table relationships are the key.
* Frank: Another motivation: Inheritence could help to add
attributes to a class that are specific to certain protocol
mapping and do not appear in the protocol neutral module.
E.g., RowStatus attributes in SNMP mappings.
* Jamie: I see this important because as more WGs move to data
modeling, it is natural to model using OO methodologies. For
example, in the IPsec Policy WG we are modeling the IPsec
configuration policy (draft-ietf-ipsp-config-policy-model-
02.txt), which derives from the Policy Core Information Model
from the Policy Framework WG. Both are modeled using OO
methodolgy and make extensive use of single inheritance. In
addition to the abstract model, the WG is defining a PIB
(draft-ietf-ipsp-ipsecpib-02.txt) and a MIB (draft-ietf-ipsp-
ipsec-conf-mib-00.txt) as concrete instantiations of the
abstract model.
* David Putzolu: As long as we avoid methods, ctors/dtors,
exceptions, etc., then single inheritance is not only useful
but feasible as well.
3.35 Abstract vs. Concrete Classes
Status: new
From: SMIng, WG
Description: SMIng should differentiate between abstract and concrete
grouping of attributes.
Motivation: This informations gives people more information how
classes can and should be used. It hinders them from misusing
abstract classes.
Discussion:
* Jamie: When doing data modeling using OO methodologies, it is
important to be able to define an abstract class, which
contains some set of attributes common to all derived classes,
but which is never meant to be instantiated by itself. Again,
an example is the IPsec policy configuration model - in that
model, we have the idea of an IPsec transform. There are
current three transforms in the model - AH, ESP, and IPCOMP.
All three share a set of attributes. Instead of repeating the
definitions of these attributes in each derived class, the
attributes are defined in an abstract base class and all three
derive from the abstract base class.
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3.36 Relationships
Status: new
From: SMIng, WG
Description: Ability to formally depict existence dependency, value
dependency, aggregation, containment, and other relationships
between attributes or grouping of attributes.
Motivation: Helps humans to understand the conceptual model of a
module. Helps implementors of MIB compilers to generate more
`intelligent' code.
3.37 Methods
Status: new
From: WG
Description: SMIng should support a mechanism to define method
signatures (parameters, return values, exception) that are
implemented on agents.
Motivation: Methods are needed to] support the definition of
operational interfaces such as found in [RFC2925] (ping,
traceroute and lookup operations). Also, the ability to define
constructor/destructor interfaces could address issues such as
encountered with SNMP's RowStatus solution.
Discussion:
* David Putzolu: If I define a class (attribute grouping?) that
derives from an abstract class, and the abstract class defines
a method with a return value of one type, but my newly defined
class has a method of the same name but returns another type,
which one is invoked? Questions like this worry me - but I can
probably answer this question if the language being used is C++
or Java. However, the goal is not to do all the things that
C++ or Java does (come up with a programming language) - it is
to make a modelling language. As such, on requirement #37 I
strongly agree with Juergen when he wrote, "I prefer to stay
away from methods at this point in time (but make the language
extensible so they might be added later)."
* Juergen: The WG charter says that we do a "next generation data
definition language for specifying network management data".
We are not supposed to create a generic (information) modelling
language. My argument for postponing methods is based on the
observation that SNMP as well as COPS currently do not support
method invocation natively and so you either have a feature in
the data definition language which you can't use in practice
(at least with SNMP and COPS-PR) or you have to do really ugly
things to emulate generic method calls on top of what SNMP and
COPS provides you.
The issue of naming scopes and how you resolve conflicts is
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important. But I do not think it is very complex to handle
this nor do I think that specifying how you solve name
conflicts makes the data definition language a programming
language. We already have rules in the SMIv2/SPPI how to
resolve conflicts if you have to import definitions with
similar names. If we have methods, we sure need more rules -
but nothing conceptually very different.
* David Putzolu again on #37 revisited: If we were to do methods,
that of course leads to the idea of exceptions. Exceptions are
a great tool for writing high quality software for a number of
reasons - but I have no clue how they relate to the case of a
data modelling language that will be mapped to on-the-wire SNMP
and COPS PDUs. How would I map a try..catch block or a throw()
to a SNMP PDU? What meaning does the idea of passing an
unhandled exception on to a higher execution context (stack
unrolling) have to a DECision message? I strongly suggest that
if methods are done that exceptions not be done. If methods
are not done, the question of exceptions becomes moot.
* Juergen: Exceptions model exceptional conditions that can
happen on the "agent" while you invoke a "method". A good
example are the INSTALL-ERRORS in the SPPI which enumerate the
exceptions that can happen while creating a new row via COPS-
PR. Note that this notion of exceptions is completely
independent from the way an application written in a particular
programming language processes exceptions. The try...catch
block is a programming language construct and we are of course
not going to specify this.
If you want an example how this can work, then please take a
look at the CORBA world. The CORBA folks define exceptions at
the IDL level. The programming language binding later says how
things are mapped to programming language constructs. And the
mappings look very different, depending on whether you use C or
Java.
3.38 Procedures
Status: new
From: WG
Description: SMIng should support a mechanism to formally define
procedures that are used by managers when interacting with an
agent.
Motivation:
3.39 Arrays
Status: new
From: WG
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Description: SMIng should allow the definition of arrays of
attributes.
Motivation:
Discussion:
* Juergen: It is unclear what this really means. Does an array
imply atomic access to the whole array? Or is it sufficient to
say this is just a short-cut for another expanding table?
* Andrea: I had viewed this only as allowing a multi-valued
attribute, not as arrays of multiple attributes. This needs to
be clarified.
* Todd A Anderson: I prefer the IDL verbage of "sequence" instead
of array since array implies something of fixed length to me.
I think that sequences are a necessary part of SMIng since I am
constantly frustrated by the proliferation of tables I have to
create to simulate sequence semantics. It seems to me that
without sequences, the number of associations would also have
to increase. I think it is just clearer and more natural for
those with a programming background to think of sequences of
data instead of breaking up the data structure into multiple
locations.
* Jamie: Is this as Andrea thought (a multi-valued attribute), or
is it a set of multiple attributes? I can see use for having a
set of multiple attributes (which is what I had thought it
was).
* Juergen: My understanding is that this refers to a multi-valued
attribute.
3.40 Composition
Status: new
From: SMIng
Description: SMIng must provide support for the composition of new
compound types from more basic (potentially compound) types.
Motivation: Simplifies the reuse attribute combination such as
InetAddressType and InetAddress pairs.
3.41 Existence Constraints
Status: new
From: WG
Description: SMIng must provide a mechanism to formally express
existance constraints.
Motivation: Existence constraints are already embedded in SMIv2 INDEX
clauses and DESCRIPTION clauses.
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3.42 Ordering Constraints
Status: new
From: WG
Description: SMIng must provide a mechanism to formally express
ordering constraints.
Motivation:
Discussion:
* Frank: What does this mean?
* Andrea: At least in some of the discussions, this "requirement"
went hand in hand with #43 (transaction constraints). IE, if
you modify something "in combination", the changes may need to
occur in a specific order (first attribute A, then attribute
B).
3.43 Attribute Transaction Constraints
Status: new
From: WG
Description: SMIng must provide a mechanism to formally express that
certain sets of attributes can only be modified in combination.
Motivation: COPS-PR always does operations on table rows in a single
transaction. There are SMIv2 attribute combinations which need to
be modified together (such as InetAddressType, InetAddress).
Discussion:
* Todd A Anderson: Could someone provide some clarity on issues
#42 and #43? An issue that seems similar to #43 is the case
when sometimes I want to execute several table changes
atomically but other times I may not want to make those changes
atomically. Is the language an appropriate place to deal with
this sort of behavior? Are there any modeling issues related
to this sort of transaction? My instinct is that there isn't
for this type of transaction but for the case where you must
always change several things atomically then the language is an
appropriate place to state that. How would the other type of
transaction be handled then?
3.44 Attribute Value Constraints
Status: new
From: WG
Description: SMIng must provide mechanisms to formally specify
constraints between values of multiple attributes.
Motivation: Constraints on attribute values [occur] where one or more
attributes may affect the value or range of values for another
attribute. One such relationship exists in IPSEC, where the type
of security algorithm determines the range of possible values for
other attributes such as the corresponding key size."
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3.45 Associations
Status: new
From: WG
Description: SMIng should provide mechanisms to explicitly specify
associations.
Motivation:
Discussion:
* Frank: What does this mean? Aren't relationships (issue #36)
the same?
* Andrea: Yes, an association is a kind of relationship but has
additional info like cardinality on the related entities.
Relationships include inheritance.
* David Putzolu on #45 and #46: These are two more ideas that on
their own make good sense, but seem to complicate the big
picture. How would cardinality be captured in a mapping to
SNMP or COPS? Pointers seems pretty easy to map to these
protocols - but where does associations fit in? These two are
elegant tools, but I think in this context, since we already
have pointers, and two pointers in a table can model an
association, simplicity says remove these two requirements.
3.46 Association Cardinalities
Status: new
From: WG
Description: Cardinalities between associations should be formally
defined.
Motivation: If you have an association between classes A and B, the
cardinality of A indicates how many instances of A may be
associated with a single instance of B. Our discussions in
Minneapolis indicated that we want to convey "how many" instances
are associated in order to define the best mapping algorithm -
whether a new table, a single pointer, etc. For example, do we
use RowPointer or an integer index into another table? Do we map
to a table that holds instances of the association/relationship
itself?
Discussion:
* See also David Putzolu's comment on issue #45.
3.47 Method Constraints
Status: new
From: WG
Description: Method definitions must provide constraints on
parameters.
Motivation:
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3.48 Table Relationships
Status: new
From: WG
Description: SMIng should support REORDERS and EXPANDS clauses.
Motivation: A REORDERS statement allows to swap indexing orders
without having to redefine the whole table. An EXPANDS statement
formally state that there is a 1:n existance relationship between
tables. This information can be used by code generators to create
more sensible implementation specific data structures.
3.49 Float Data Types
Status: new
From: WG, SMIng
Description: SMIng should support the base data types Float32,
Float64, Float128.
Motivation: Missing base types can hurt later on, because they cannot
be added without changing the language, even not as an SMIng
extension. Lesson learnt from the SMIv1/v2 debate about
Counter64/Integer64/...
Discussion:
* Todd A Anderson: I am glad to see that the spec includes float
data types in the language. I find these types especially
useful for TSPECs and fractional link bandwidth partitioning.
3.50 Compliance and Conformance
Status: basic
From: SMIv2, SPPI
Description: SMIng should provide a mechanism for compliance and
conformance specifications for protocol- independent definitions
as well as for protocol mapping.
Motivation: This capability exists in SMIv2 and SPPI. In SMIng we
have the ability to express much of this information at the
protocol-independent layer, this reducing redundant information.
Some compliance or conformance information may be protocol-
specific, therefore we also need the ability to express this
information in the mapping.
3.51 Categories of Modules
Status: new
From: Individual
Description: The SMIng documents should give clear guidance on which
kind of information (wrt generality, type/class/extension/..)
should be put in which (kind of a) module.
Motivation: E.g., in SMIv2 we don't like to import Utf8String from
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SYSAPPL-MIB, but we also do not like to introduce a redundant
definition.
A module review process should probably be described that ensures
that generally useful definitions do not go into device or service
specific modules.
Bad experience with SMIv2.
3.52 Language Extensibility
Status: new
From: SMIng
Description: The language should have characteristics, so that future
modules can contain information of future syntax without breaking
original SMIng parsers.
Motivation: E.g., when SMIv2 introduced REFERENCEs it would have been
nice if it would not have broken SMIv1 parsers.
Achieve language extensibility without breaking core
compatibility.
3.53 Length of Identifiers
Status: should
From: SMIng
Description: The allowed length of the various kinds of identifers
should be extended from the current `should not exceed 32' (maybe
even from the `must not exceed 64') rule.
Motivation: Reflect current practice of definitions.
3.54 Why Are So Many SMIv1/v2 So Error Tolerant?
Status: should
From: Individual
Description: It should be clearly stated that parser implementations
which accept input that does not conform to the SMIng language
rules are not compliant.
Motivation: SMIv1/v2 parsers are tolerant, because MIB editors do not
get SMI right, because it builds on hardly available obsolete
ASN.1 CCITT specifications. With SMIng there is a chance to get
the syntax clearly and self-contained defined, so that there is no
excuse for errors and parser implementations become more
consistent. (Who would expect that a C compiler is tolerant about
a missing semicolon?)
Discussion:
* David H.: I think the reality of the situation is that
developers write few mibs, but write much C code. There are
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few developers who understand mib syntax, and I don't expect to
see that improve even if we use a non-ASN.1 langauge, and
parsers are classified as non-compliant. I won't oppose this
suggestion, but I doubt it will solve the problem.
* Frank: If parsers are (available and) forced to be verbatim
about errors then MIB authors have simple tools to validate
their modules. C programs are correct because they must be
compiled to be useful and because C compilers are strict. I
agree, that many people are not really familiar with MIB syntax
because they write much less MIB modules than C (or other)
code. And I agree that a non-ASN.1 looking syntax would not
help significantly.
3.55 Core Language Keywords vs. Defined Identifiers
Status: should
From: SMIng
Description: In SMIv1/v2 things like macros or some(!) types have to
be imported from SMI modules. People are continuously confused
about what has to be imported (imagine `typedef' would have to be
#included in a C program) and what the difference between those
SMI modules and usual modules is.
Motivation: Reduce confusion. Clarify the set of language keywords.
3.56 i18n
Status: new
From: Individual
Description: Informational text (DESCRIPTION, REFERENCE, ...) should
allow i18nized encoding (UTF8? others?).
Motivation: There has been some demand for i18n in the past.
Discussion:
* David H.: Fred Baker made it very clear as IESG chair that all
documents submitted for standards advancement should be done in
English to ensure a large enough body of reviewers exists to
provide industry-wide review.
I fear making mib descriptions i18n capable would encourage
development of mibs written in languages that most developers
could not read, and that would hurt interoperability.
I understand that it is frustrating for those who do not speak
English as their primary language to be forced to use English.
However, the purpose of standards is to improve
interoperability.
* Randy: Many MIBs are never subjected to the standards process.
A specification should be intelligible to the community of
developers and users that will use that MIB. Many MIBs never
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see use outside the organizations that defined them.
Let the RFC submission / publication process do its job of
weeding out horrible things like the name of the city where I
live, and tricky things like non-English words and phrases that
fit into seven-bit ASCII. We don't have to replicate that
service in our language definition, just as our language
definition doesn't need to recapitulate the I-D and RFC rules
for page breaks.
We are not doing the world a service by preventing
organizations from using the tools we define to develop
specifications that their developers can understand.
3.57 Special Characters in Texts
Status: new
From: Individual
Description: Allow an escaping mechanism to encode characters like
double quotes or explicit NLs in texts like DESCRIPTIONs or
REFERENCEs.
Motivation: Otherwise, it's not possible to represent the contents of
the SMIng `abnf' statement correctly: it can contain literal
characters enclosed in double quotes.
3.58 Mapping Modules to Files
Status: new
From: SMIng
Description: There should be a clear statement how SMIng modules are
mapped to files (1:1, n:1?) and how files should be named (by
module name in case of 1:1 mapping?).
Motivation: SMI implementations show up a variety of filename
extensions (.txt, .smi, .my, none). Some expect all modules in a
single file, others don't. This makes it more difficult to
exchange modules.
Discussion:
* David H.: I think this is two separate requirements with
different potential effects on the community and should be
described separately.
I have no issue with deciding that there should only be one
module per file, or that more than one can be bundled together.
(I prefer the single module per file to make updates easier)
I am concerned that requiring specific filename formatting may
prevent files from being used on some operating systems. I
gladly accept that the documents should recommend, but not
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require, a consistent format for naming mib files. But I would
consider it a bad thing to have a compiler refuse to compile a
mib because the filename doesn't match the mib name, or
whatever.
3.59 Comments
Status: should
From: SMIng
Description: The syntax of comments should be well defined,
unambiguous and intuitive to most people, e.g., the C++/Java `//'
syntax.
Motivation: ASN.1 Comments (and thus SMI and SPPI comments) have been
a constant source of confusion. People use arbitrary lengthy
strings of dashes (`-----------') in the wrong assumption that
this is always treated as a comment. Some implementations try to
accept these syntactically wrong constructs which even raises
confusion. We should get rid of this problem.
3.60 Simple Grammar
Status: new
From: SMIng
Description: The grammar of the language should be as simple as
possible. It should be free of exception rules. A measurement of
simplicity is shortness of the ABNF grammar.
Motivation: Ease of implementation. Ease of learning/understanding.
3.61 Place of Module Information
Status: should
From: SMIng
Description: Module specific information (organization, contact,
description, revision information) should be bound to the module
itself and not to an artificial node (like SMIv2 MODULE-IDENTITY).
Motivation: Keep module information where it belongs.
Discussion:
* David H.: I don't understand what is being requested here. Is
the (like SMIv2 MODULE-IDENTITY) and example if what is
desired, or an example what is not desired? Where does module
information belong in the proposer's eyes?
* Frank: I'm sorry for the confusion. I try to be more precise:
In SMIv2 and SPPI the MIB/PIB author has to put some module
meta information in a specific macro (MODULE-IDENTITY) which is
registered with an OID although this registration is not useful
for any purpose. The proposal is to let SMIng (a) not register
module meta information in the registration tree and (b) not
introduce a new macro/statement wrapping the module meta
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information, since the module itself is the appropriate
container.
3.62 Fully Qualified Identifiers
Status: should
From: SMIng
Description: To reference multiple identifiers with the same name but
imported from multiple modules a qualifying mechanism, e.g.,
`module::name', is needed. It should be manifested in the
grammar. (SMI and SPPI do support it already because of their
ASN.1 derivation, but many implementation fail to handle this
correctly.)
Motivation: Unambiguous references to identifiers.
3.63 Readable Revision Date Representation
Status: should
From: SMIng
Description: The SMI notation of revision dates consists of 11 or 13
characters, e.g. 199602282155Z, which is difficult to parse for
humans. The trailing `Z' which represents GMT is superfluous,
since no other timezone is allowed.
Motivation: SMIng should support a nicer notation, e.g. based on ISO
8601 representation: 1996-02-28 21:55 or simply 1996-02-28 since
time information is not relevant in almost any case.
Human readability of date and time information.
3.64 Make Status Information Optional
Status: new
From: SMIng
Description: SMI and SPPI definitions must have a status information
(current, obsolete, deprecated). SMIng should make the status
clause optional with a default of `current'.
Furthermore, clear statements are required on constraints of
status information of related definitions, e.g., a current
attribute definition must not make use of an obsolete defined
type, etc. Note, that this is problematic with definitions from
multiple independently evolving modules.
Motivation: Make definitions more compact. Hide redundant
information.
Discussion:
* David H.: I believe this is a bad idea if we allow inheritance
and independent evolution of modules. It is very possible that
a base class could be declared obsolete, but the derived
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classes would still incorrectly default to current. Some might
conclude that they cannot obsolete something that somebody
might have derived from, so they leave it marked as current.
I think defaulting to current will be very confusing to people
and the cure is worse than the illness. We need to make our
standards unambiguous, much more than we need to eliminate a
little redundancy.
* Frank: Status information wrt inheritance is a general problem
as already stated in the description section. It does not
matter whether the status clause is optional with a well
defined default status if absent or whether the status clause
is mandatory. There is no problem of ambiguity.
* Jamie: Am I right in assuming that #64 (Make Status Information
Optional) refers to status information that is most useful to a
human? For example, if something is deprecated, a compiler
could inform the user that they are depending on/deriving
from/referenceing something that has been deprecated in a
manner similar to how the Java compiler does. If we go down
the path of keeping the status information for the purpose of
providing meaningful information from compilers, do we go down
the road of also supplying additional information. For
example, in the case of a deprecated class that is inherited
from, should there also be information that states the name of
the new class that should be inherited from instead?
* Juergen: Issue #64 only deals with the proposal to make the
status statement in the language optional in order to make
definitions more compact and easier to read for humans. Issue
#64 does not propose to change the semantics of the status
values as they are used in the SMIv2 or the SPPI.
What compilers do with the status values is implementation
specific. Sure, a good compiler should warn if current
definitions depend on deprecated or obsolete definitions. I
personally would leave it to the MIB authors who deprecates
definitions to explain the situation in the description clause.
I personally prefer to not add language complexity in this case
as the benefit does not seem clear/convincing to me.
3.65 Units and Default Values of Defined Types
Status: new
From: SMIng
Description: In SMIv2 OBJECT-TYPE definitions may contain UNITS and
DEFVAL clauses and TEXTUAL-CONVENTIONs may contain DISPLAY-HINTs.
In a similar fashion units and default values should be applicaple
to defined types and format information should be applicable to
attributes.
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Motivation: Some MIBs introduce TCs such as KBytes and every usage of
the TC then specifies the UNITS "KBytes". It would simplify
things if the UNITS were attached to the type definition itself.
Note that SMIng must clarify the behavior, if an attribute uses a
defined type and both, the attribute and the defined type, have
units/default/format information.
3.66 Arbitrary Unambiguous Identities
Status: basic
From: SMI
Description: SMI allows to use OBJECT-IDENTITIES to define
unambiguous identies without the need of a central registry. SMI
uses OIDs to represent values that represent references to such
identities. SMIng needs a similar mechanism (a statement to
register identities, and a base type to represent values),
although OIDs are probably not present in the core language.
Motivation: SMI Compatibility.
3.67 Remove OIDs from the Core Language
Status: new
From: SMIng
Description: While in SMI and SPPI definitions of attributes are
bound to OIDs, SMIng should not use OIDs for the definition of
classes, class attributes, events, etc. Instead, SNMP and COPS-PR
mappings should assign OIDs to the mapped items.
Motivation: OIDs of synonymous attributes are not the same in SMI and
SPPI definitions. Hence, they must not appear in protocol neutral
definitions.
3.68 Module Namespace
Status: new
From: WG
Description: Currently the namespace of modules is flat and there is
no structure in module naming causing the potential risk of name
clashes. Possible solutions:
* Assume module names are globally unique (just as SMIv1/v2),
just give some recommendations on module names.
* Force all organizations, WGs and vendors to apply a name prefix
(e.g. CISCO-GAGA-MIB, IETF-DISMAN-SCRIPT-MIB?).
* Force enterprises to apply a prefix based on the enterprise
number (e.g. ENT2021-SOME-MIB).
* Put module names in a hierarchical domain based namespace (e.g.
DISMAN-SCRIPT-MIB.ietf.org).
Motivation: Reduce risk of module name clashes.
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3.69 Problem: Where to Put Constraints Required by the Protocol?
Status: new
From: Individual
Description: Some constraints have to be fulfilled in order to not
violate protocol limitation. E.g., OIDs are limited to 128 sub-
identifiers. If strings are proposed to be used for indexing,
should their lengths be limited in the protocol neutral model or
in the SNMP mapping?
class Script {
attribute String owner { ... }; // limit to 32 octets?
attribute String name { ... }; // limit to 32 octets?
...
unique (owner, name);
};
snmp {
table smScriptTable {
oid smScriptObjects.3;
index (owner, name);
implements Script {
object smScriptOwner owner; // limit to 32 octets?
object smScriptName name; // limit to 32 octets?
...
};
};
};
Motivation: [This is just an open question.]
3.70 Problem: Phrasing Descriptions
Status: new
From: Individual
Description: It can be a real pain for SNMP people to (re)phrase
DESCRIPTIONs in a protocol neutral way. Exercise: Try to rephrase
this DESCRIPTION:
ifTableLastChange OBJECT-TYPE
SYNTAX TimeTicks
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime at the time of the last creation
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or deletion of an entry in the ifTable. If the number
of entries has been unchanged since the last re-
initialization of the local network management
subsystem, then this object contains a zero value."
::= { ifMIBObjects 5 }
Motivation: [This is just an open question.]
3.71 Problem: Mapping Protocol Specific Attributes
Status: new
From: Individual
Description: Some attributes are only meaningful in a specific target
domain, e.g., RowStatus in SNMP. They should not be specified in
protocol neutral SMIng models. They have to be added to classes
in the SNMP mapping module. This could be achieved by using
inheritence: A protocol specific class can be inherited from the
protocol neutral class adding the relevant RowStatus attributes in
the SNMP mapping module. In the same module, the SNMP mapping is
done based on the refined classes.
Further problems can occur, when classes should be modeled this
way that represent original SMIv2 tables that contain objects with
mixed semantics, e.g. a RowStatus object that is (mistakenly)
also used to represent a row's enabled/disabled status.
Motivation: [This is just an open question.]
3.72 Hyphens in Identifiers
Status: should
From: SMIng
Description: There has been some confusion whether hyphens are
allowed in SMIv2 identifiers: Module names are allowed to contain
hyphens. Node identifiers usually are not. But for example `mib-
2' is a frequently used identifier that contains a hyphen due to
its SMIv1 origin, when hyphen were not disallowed. Similarly, a
number of named numbers of enumeration types contain hyphens
violating an SMIv2 rule.
Motivation: SMIng should simply allow hyphens in all kinds of
identifiers. No exceptions.
Reduce confusion and exceptions. Requires, however, that
implementation mappings properly quote hyphens where appropriate.
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3.73 The Set of Spec Documents
Status: new
From: SMIng
Description: SMIv2 is defined in three documents, based on an
obsolete ITU ASN.1 specification. SPPI is defined in one
document, based on SMIv2. The core of SMIng should de defined in
one document, independant of external specifications.
Motivation:
3.74 Allow Refinement of All Definitions in Conformance Statements
Status: must
From: Individual
Description: SMIv2, RFC 2580, Section 3.1 says:
The OBJECTS clause, which must be present, is used to
specify each object contained in the conformance group.
Each of the specified objects must be defined in the same
information module as the OBJECT-GROUP macro appears, and
must have a MAX-ACCESS clause value of
"accessible-for-notify", "read-only", "read-write", or
"read- create".
The last sentence forbids to put a not-accessible INDEX object
into an OBJECT-GROUP. Hence, you can not refine its syntax in a
compliance definition. For more details, see
http://www.ibr.cs.tu-bs.de/ietf/smi-errata/
Motivation: This error should not be repeated in SMIng.
Prevent SMIv2 errata.
Discussion:
* David H.: I am not aware that this has been a problem except
for one person. I am concerned that the requested requirement
be that "All Definitions" must be allowed to be refined rather
than to request that the one specific problem be addressed.
3.75 Referencing a Group of Instances of a Class
Status: align
From: Individual
Description: PIB and MIB row attributes reference a group of entries
in another table. This semantic needs to be formalized.
Motivation: SPPI formalizes this feature using TagId and
TagReferenceId semantics (see draft-ietf-diffserv-pib-03.txt).
SMI also uses these semantics without any formal notation (see
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SNMP-TARGET-MIB in RFC2273).
Discussion:
* David H.: Is this already covered by #46 Association
Cardinalitites? Do we need to separate the formal
specification of cardinality from its use here for
associations?
4. Conformance and Capability Reporting
[TBD. See also reqs-00.]
5. Glossary of Terms
Association: A relationship between the instances of classes.
Associations are typically binary, and convey the semantics of the
class' connection.
Aggregation: A whole-part relationship.
Attribute: An atomic or composite data type that is fully described,
typed, uniquely named, and optionally bounded via constraints. It
represents the common characteristics or features of an object.
Class: A set of one or more attributes and methods, that can
participate in associations and that can inherit properties from
parent classes to optimize data definitions. It represents a
grouping or typing of "like" objects.
Composition: The ability to define a class using the names of other
classes, as though these "contained" classes were data types. The
result is to include one class' property set within another class'
definition. (See also "containment.")
Constraint: A mechanism for bounding an attribute or class value to
allowed values/ranges/targets/bitmaps etc. There are both data
level and semantic constraints.
Containment (1): An association that describes the ownership, scoping
and naming of instances within the context of another object.
Containment (2): The ability to contain a class' property set within
another class' definition. This is referred to as "class
composition" in this document.
Definition Name: Unique name used to identify an attribute or class
definition.
Event: Occurrences which should be reported or which will result in a
change of state.
Index: (See "Instance Name.")
Instance Name: One or more attributes of a class whose value(s)
uniquely identify an instance. This is also known as an "index"
or "key."
Interface: (See "method signature.")
Key: (See "Instance Name.")
Method: The specification of a behavior or operation, having a
specific signature, included in a class definition.
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Method Signature: The definition of a method's name, return value,
and input/output parameter list. This is also known as an
"interface."
Object-Oriented Modeling: Representation of a domain of discourse by
grouping or typing its objects (into "classes"). This is
accomplished by identifying common characteristics and features of
the objects (properties), relationships (associations) and ability
to affect state changes (methods).
6. Security Considerations
This document defines requirements for a language with which to write
and read descriptions of management information. The language itself
has no security impact on the Internet.
7. Acknowledgements
Special thanks to Dave Durham, whose work on the original NIM
(Network Information Model) draft was used in generating this
document.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Structure of
Management Information Version 2 (SMIv2)", STD 58, RFC 2578,
April 1999.
[3] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Textual
Conventions for SMIv2", STD 58, RFC 2579, April 1999.
[4] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Conformance
Statements for SMIv2", STD 58, RFC 2580, April 1999.
[5] , ., Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Management Information Base for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1907, January 1996.
[6] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight
Directory Access Protocol (v3): Attribute Syntax Definitions",
RFC 2252, December 1997.
[7] White, K., "Definitions of Managed Objects for Remote Ping,
Traceroute, and Lookup Operations", RFC 2925, September 2000.
[8] McCloghrie, K., Fine, M., Seligson, J., Chan, K., Hahn, S.,
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Sahita, R., Smith, A. and F. Reichmeyer, "Structure of Policy
Provisioning Information (SPPI)", draft-ietf-rap-sppi-06.txt,
April 2001.
[9] Fine, M., McCloghrie, K., Seligson, J., Chan, K., Hahn, S.,
Sahita, R., Smith, A. and F. Reichmeyer, "Framework Policy
Information Base", draft-ietf-rap-frameworkpub-04.txt, April
2001.
[10] <http://www.ibr.cs.tu-bs.de/projects/sming/issues.html>
Authors' Addresses
Andrea Westerinen
Cisco Systems
725 Alder Drive
Milpitas, CA 95035
USA
EMail: andreaw@cisco.com
Chris Elliott
Cisco Systems
7025 Kit Creek Road
Research Triangle Park, NC 27709
USA
EMail: chelliot@cisco.com
Juergen Schoenwaelder
TU Braunschweig
Bueltenweg 74/75
38106 Braunschweig
Germany
Phone: +49 531 391-3289
EMail: schoenw@ibr.cs.tu-bs.de
URI: http://www.ibr.cs.tu-bs.de/
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Frank Strauss
TU Braunschweig
Bueltenweg 74/75
38106 Braunschweig
Germany
Phone: +49 531 391-3266
EMail: strauss@ibr.cs.tu-bs.de
URI: http://www.ibr.cs.tu-bs.de/
Jamie Jason
Intel Corporation
MS JF3-206
2111 NE 25th Ave.
Hillsboro, OR 97124
USA
EMail: jamie.jason@intel.com
Walter Weiss
Ellacoya Networks
7 Henry Clay Dr.
Merrimack, NH. 03054
USA
EMail: wweiss@ellacoya.com
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