ETSI TCRTR 046 ed.1 (1996-08)

SLOVENSKI STANDARD
01-april-2005
3UDYLODLQSRVWRSNL]DNQMLåQLFR$615D]OLþLFD
ASN.1 library rules and procedures; Version 1
Ta slovenski standard je istoveten z: TCRTR 046 Edition 1
ICS:
33.020 Telekomunikacije na splošno Telecommunications in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

ETSI TCR-TR 046
TECHNICAL COMMITTEE August 1996
REFERENCE TECHNICAL REPORT
Source: ETSI TC-SPS Reference: DTR/SPS-02026
ICS: 33.100.60
Key words: ASN.1
ASN.1 library rules and procedures;
Version 1
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
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Tel.: +33 92 94 42 00 - Fax: +33 93 65 47 16
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1996. All rights reserved.

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TCR-TR 046: August 1996
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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TCR-TR 046: August 1996
Contents
Foreword .5
Introduction.5
1 Scope .7
2 References.7
3 Definitions and abbreviations .8
3.1 Definitions .8
3.2 Abbreviations .8
4 General concept.8
4.1 Overview .8
4.2 Library rules .9
4.3 Library procedures.10
4.4 Library maintenance organization.11
4.5 Conclusion .11
5 Rule definitions.12
5.1 Library rules .12
5.1.1 Library structure .12
5.1.2 Library contents.12
5.2 Library index rules.13
5.2.1 Library index structure.14
5.2.2 Library index contents .14
5.3 Library Maintenance Organization (LMO) rules .14
5.3.1 Maintaining the library .14
5.3.2 Maintaining the library index.14
5.3.3 Library user support .15
5.3.4 Version handling.15
6 Procedure definitions.15
6.1 Request.16
6.1.1 Register .16
6.1.2 De-register.16
6.1.3 Modify.17
6.1.4 Remove.18
6.2 Execution of multiple requests.18
6.3 Version handling .18
6.3.1 New version of this TCR-TR .18
6.3.2 New version of ETSI-LIB.19
6.3.3 New version of LIB-INDEX.19
6.4 Naming convention of documents .19
7 Managing documents.20
Annex A: Summary of rules.21
A.1 List of rules applicable to the ASN.1 library.21
Annex B: Library procedures .23
B.1 BNF notation of the library procedures.23
B.2 Procedural semantics.23
B.2.1 Execution of Request.23

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B.2.2 Execution of Register . 24
B.2.3 Execution of De-register. 24
B.2.4 Execution of Modify. 24
B.2.5 Execution of Remove . 25
Annex C: Examples. 26
C.1 Introduction. 26
C.1.1 General concept. 26
C.1.2 About this annex. 26
C.1.3 Intended readers . 27
C.2 Background. 27
C.3 Examples. 27
C.3.1 Example 1 . 27
C.3.2 Example 2 . 28
C.3.3 Example 3 . 29
C.3.4 Example 4 . 30
C.3.5 Example 5 . 31
Annex D: Template for ETSI-LIB . 33
D.1 Introduction to the ETSI-LIB template . 33
D.2 Scope. 33
D.3 Normative references . 33
D.4 Definitions and abbreviations. 33
D.4.1 Definitions. 33
D.4.2 Abbreviations. 34
D.5 ETSI library definition. 34
D.5.1 ASN.1 module definitions of the library version 1.0. 34
D.5.1.1 Interface module. 34
D.6 Annex A (informative): Expanded source for version 1.0 . 35
D.7 Annex B (informative): Cross reference for version 1.0 . 35
D.8 Annex C (informative): Bibliography . 35
Annex E: Template for LIB-INDEX . 36
E.1 Introduction to the LIB-INDEX template . 36
E.2 Scope. 36
E.3 References . 36
E.4 Definitions and abbreviations. 36
E.4.1 Definitions. 36
E.4.2 Abbreviations. 37
E.5 ASN.1 library index . 37
E.6 Annex A (informative): Bibliography . 37
History. 38

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Foreword
This Technical Committee Reference Technical Report (TCR-TR) has been produced by the Signalling
Protocols and Switching (SPS) Technical Committee (TC) of the European Telecommunications
Standards Institute (ETSI) following consultation with all TC/STC Chairmen.
A TCR-TR is a deliverable for use inside ETSI which records output results of ETSI Technical Committee
(TC) or Sub-Technical Committee (STC) studies which are not appropriate for European
Telecommunication Standard (ETS), Interim European Telecommunication Standard (I-ETS) or ETSI
Technical Report (ETR) status. They can be used for guidelines, status reports, co-ordination documents,
etc. They are to be used to manage studies inside ETSI and shall be mandatorially applied amongst the
concerned TCs. They shall also be utilized by the TC with overall responsibility for a study area for co-
ordination documents (e.g. models, reference diagrams, principles, structures of standards, framework
and guideline documents) which constitute the agreed basis for several, if not all, TCs and STCs to
pursue detailed standards.
Introduction
Reuse of common application elements
The growing complexity of telecommunication systems requires advanced methods for design,
implementation and testing as well as maintenance. Telecommunication products often interact with
others by exchanging messages or by sharing some common property. Errors, omissions or common
property mismatches in telecommunication standards are often costly to correct. Moreover, if errors are
not detected, and permeate in telecommunication products, they may lead to loss of property and
revenue. Therefore it is important, to assure that telecommunication standards interact correctly and that
they do share as many common properties as possible.
International standardization organizations have developed formal notations, such as Abstract Syntax
Notation One (ASN.1) in CCITT Recommendation X.208, for the definition of messages exchanged
between telecommunication systems. The use of ASN.1 in specifications of telecommunication systems
has increased heavily over the last years. As different telecommunication standards may define the same
common application element, one definition in each standard, several definitions for a single element will
exist. This will lead to double-definitions and possibly complicated interworking between standards as one
standard may change an intended common definition in some later stage.
The problem with double-definitions and complicated interworking between standards can be solved by
setting up a centralized ASN.1 library and a corresponding library index. The library will contain all
definitions of common property elements and all standards can use that definition by reference. The
library index will keep track of the use of the library elements. To accomplish this centralized library, and
the library index, three topics have to be discussed:
Topic 1: What is the library contents and how is it structured?
Topic 2: How are changes to the library performed?
Topic 3: Who shall maintain the library?
Topic 1 aims the domain of rules. There have to be rules stating what shall be in the library and what shall
not. Of course, only "correct" ASN.1 shall appear in the library but other requirements have to be met as
well! The answer to topic 1 will be a collection of rules that, when applied, preserve the soundness of the
library and the correctness of its contents.
Topic 2 covers the domain of procedures. The procedural behaviour when applying the rules, changing
the library contents or maintaining the library has to be defined.
Topic 3 aims the domain of responsibility. Subjects as maintenance, ownership and version handling of
the library and the library index must be defined.
The need to ease the potential reuse of these common property definitions and to detect multiple
definitions of common application elements is obvious. Therefore, rules, procedures and responsibilities
have to be defined and implemented in order to support reuse of common application elements as well as
detection of multiple definitions.

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This TCR-TR presents a set of rules and procedures that support the reusability of common application
elements. Following these rules and procedures will ensure that no duplicate definitions of common
application elements will exist. The maintenance of telecommunication standards and test specifications
will be easier, thereby guaranteeing that exactly the same common properties will be shared. This may
lead to important cost reduction in the development and maintenance of telecommunication standards.
About this TCR-TR
This TCR-TR is structured as follows:
Clauses 1 to 3 contain the scope of this TCR-TR; the references, definitions and abbreviations used in this
TCR-TR.
Clause 4 describes the general concept in terms of needed rules and procedures. The ownership and
maintenance of the library is discussed in subclause 4.4.
Clause 5 defines a set of rules that preserves a sound and valid library.
Clause 6 defines a set of procedures that can be applied to the library and the library index.
Clause 7 describes a procedure for managing the corresponding ETS 300 655 and ETR 210 by using
templates defined in this TCR-TR.
The following annexes are provided in this TCR-TR:
- Annex A gives a summary of the rules defined in this TCR-TR;
- Annex B gives a BNF description and the procedural semantics of the library procedures;
- Annex C is a collection of examples considering the usage of the library and the library index;
- Annex D presents a template for ETS 300 655;
- Annex E presents a template for ETR 210.
Intended audience
This TCR-TR targets the group of persons which will maintain the ASN.1 library and the ASN.1 library
index.
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1 Scope
The main objective of this Technical Committee Reference Technical Report (TCR-TR) is to establish a
set of rules and procedures applicable to the ASN.1 library as well as to the ASN.1 library index. It also
defines the scope for a group, responsible of the library and its maintenance.
The main assignment of the ASN.1 library and the ASN.1 library index is to support the reuse of common
application elements as well as to detect multiple definitions within ETSI protocol standards. Therefore,
this TCR-TR is restricted to define rules and procedures for common application elements defined and
used within ETSI. However, any common application element defined outside ETSI may be included in the
ASN.1 library. This implies that these external elements will be redefined in the ASN.1 library as, from an
ETSI point of view, definitions of common application elements always shall reside in the ASN.1 library. In
parallel, the ASN.1 library index will keep track of such (external) definers.
ASN.1 definitions have in most cases limited applicability outside the protocol they define. To achieve a
more extensive use of the definitions residing in the ASN.1 library and thereby support the design of new
protocols, the definitions residing in the ASN.1 library shall be as generic as possible.
This TCR-TR gives guidance for contributions to the ASN.1 library. While ETSI as a whole will gain more
consistent and interoperable ASN.1 protocols by the adoption of the rules and procedures defined herein,
this TCR-TR does not force or restrict in any way a committee to participate in the process of increased
reusability.
Throughout this TCR-TR the term "library" denotes the ASN.1 library, the term "library index" denotes the
ASN.1 library index and the term "library element" denotes an ASN.1 definition residing in the library.
2 References
This TCR-TR incorporates by dated and undated reference, provisions from other publications. These
references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this
TCR-TR only when incorporated in it by amendment or revision. For undated references the latest edition
of the publication referred to applies.
[1] CCITT Recommendation X.208 (1988): "Specification of abstract syntax
notation one (ASN.1)" (technically aligned with ISO 8824)".
[2] ITU-T Recommendation X.680 (1994): "Information technology - Open System
Interconnection - Abstract Syntax Notation One (ASN.1): Specification of Basic
Notation" (also published as ISO/IEC 8824-1).
[3] ETR 060 (1995): "Signalling Protocols and Switching (SPS); Guidelines for using
Abstract Syntax Notation One (ASN.1) in telecommunication application
protocols" (to be endorsed as TCR-TR 047).
[4] TCR-TR 019: "Signalling Protocols and Switching (SPS); evaluation of ASN.1
tools for use as syntax and semantic checkers".
[5] ETS 300 351 (1994): "ETSI object identifier tree; Rules and registration
procedures".
[6] ETS 300 655: "ASN.1 library definition".
[7] ETR 210: "ASN.1 library index".

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3 Definitions and abbreviations
3.1 Definitions
For the purposes of this TCR-TR, the following definitions apply:
ASN.1 definition: A definition resulting from one of the alternatives for an ASN.1 "Assignment" as defined
by ITU-T Recommendation X.680 [2].
common application element: An ASN.1 type definition or ASN.1 value definition that can or is
commonly used in other ASN.1 modules.
ETSI-LIB: The most recent ETS containing the current version of the ASN.1 library, hence
ETS 300 655 [6].
LIB-INDEX: The most recent ETR containing the current version of index to the ASN.1 library, hence
ETR 210 [7].
LIB-R&P: This term refers to the rules and procedures defined for the ASN.1 library, hence the most
recent version of this TCR-TR.
Library Maintenance Organization (LMO): An organization maintaining the ASN.1 library and the ASN.1
library index.
library module: An ASN.1 module containing one or several Common Application Element definitions.
library procedures: A set of procedures that modify the ASN.1 library as well as the ASN.1 library index
in terms of contents and structure.
library rules: A set of rules applicable to the ASN.1 library that preserves the soundness and structure of
the library.
validated ASN.1: ASN.1 definitions are valid if they conform with the guidelines defined in ETR 060 [3].
For the purpose of this TCR-TR these guidelines are to be considered as binding. Validation is done by
the LMO.
3.2 Abbreviations
For the purposes of this TCR-TR, the following abbreviations apply:
ASN.1 Abstract Syntax Notation One
BNF Backus-Naur Form
ETR ETSI Technical Report
ETS European Telecommunication Standard
LIB Library
LMO Library Maintenance Organization
R&P Rules and Procedures
4 General concept
4.1 Overview
The use of ASN.1 when defining application elements has increased over the last years. It is therefore
proposed to collect commonly used application elements defined in ASN.1, register them and store them
in a centralized library. The advantage of this centralized library is twofold:
- the collection and registration of ASN.1 definitions ensures the reusability of these elements.
Duplicate definitions in different documents that bear the potential risk of inconsistencies are
avoided;
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- the formalized collection procedures for ASN.1 definitions only allow the registration of elements
that are sound according to some rules. Hence the correctness and soundness of the ASN.1 library
is preserved and thereby any use of library items.
To accomplish such a centralized library three topics have to be discussed:
- library rules;
- library procedures;
- library maintenance.
The following subclauses aim these topics and explain the scope and the domain of each topic, showing
that all topics have to be discussed and the answers have to be implemented to set up a centralized
ASN.1 library.
4.2 Library rules
Library rules define the boundary of the library and its contents as well as its structure. In this TCR-TR,
rules are defined as statements that define and restrict the contents of the library and its boundaries.
Common Application Element candidates
Rules
R
?
ASN.1 Library
Figure 1: Library rules and their relation to the ASN.1 library:
EXAMPLE: Is this definition, suggested for the library, validated ASN.1?
A rule is of static nature. Applying rules to the above question will result in an answer that has to be strictly
"Yes" or "No". A "No" will lead to the rejection of the above suggestion.
NOTE: Library rules are statements that ensure the correctness of the library and the library
index.
The rules stated in this TCR-TR shall be obeyed. The addition or change of rules should always be
reflected by a new edition of this TCR-TR.
The rules defined in this TCR-TR may be applicable to a possible electronic (informative) library existing in
parallel with ETSI-LIB.
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4.3 Library procedures
The need for defining procedures to maintain the library is quite obvious. Without pre-defined procedures
one can not guarantee a sound library and a sound maintenance. While a rule is of a static nature, a
procedure has a more dynamic behaviour. A procedure simply states how to get from state A to state B,
where state A and B are both valid states.
Common Application Element candidates
Rules and Procedures
R P
?
ASN.1 Library Index ASN.1 Library
Figure 2: Library procedures and their relation to the library and the library index
EXAMPLE: How is an element added to the library?
If there exists a library, valid according to some rules, the question stated above is a request to move the
library from a valid state to another valid state with one element added. The procedural behaviour of this
request can now be seen as a sequential execution of a set of rules.
As some procedures need to have knowledge of the contents of the library, a library index has to be set
up in parallel with the actual library. While the library only contains library elements, the index contains a
list of what is in the library, who is using a particular library element, etc. The index has rules and
procedures attached to it just as the library.
NOTE 1: Library procedures are operations on the library index and the library.
NOTE 2: From a global point of view, the library index exists only for internal use.
The procedures described in this TCR-TR may be applicable to a possible electronic (informative) library
existing in parallel with ETSI-LIB.

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4.4 Library maintenance organization
Having rules and procedures defined for validating the library and the library index as well as for
maintaining the library, the need for a centralized organization performing these procedures and obeying
the rules is obvious and clear. Any user of the library has to know whom to target a library request to.
Therefore, the responsibility for collecting, verifying and registration these common application elements
as well as maintaining the centralized library shall be held by a LMO.
The scope of the LMO is to act as the owner and maintainer of the library. Through them change requests
shall be addressed (i.e. adding or deleting library elements). Any change to the library shall be done
according to the rules and procedures defined in this TCR-TR.
Rules and Procedures Common Application Element candidates
R P
Library users
Library Maintenance Organisation
ASN.1 Library Index ASN.1 Library
Figure 3: The LMO in its context
4.5 Conclusion
The LMO will achieve a sound ASN.1 library with a valid contents by using the rules and procedures
defined in this TCR-TR. Of course, that organization may change the rules, procedures or their scope of
responsibility at any time. However, these changes shall lead to a new version or a replacement of this
TCR-TR. One single document containing all rules and procedures for the LMO will ease the duty of that
organization.
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5 Rule definitions
The rules stated in this TCR-TR shall be valid for any version of the library and the library index at any
time. No other rules exist for the library or the library index.
5.1 Library rules
This subclause and any following subclauses define a set of rules applicable to the ASN.1 library and its
index.
Rule 1: The library shall be an ETS, both concerning contents and structure.
The rule is motivated by reasons of use ability. A reference to a library item can be made from an ETS. An
ETS can not reference non-standardized elements, therefore the library has to be an ETS.
5.1.1 Library structure
Rule 2: The ASN.1 library will be paper based.
The rule is motivated by the fact that all standards (ETSs) are paper based.
NOTE: An electronic version of the library may exist in parallel with the paper-based version.
Rule 3: The library shall consist of a collection of ASN.1 modules into which related library elements are
grouped.
The rule is motivated by reasons of clarity.
Rule 4: The library and all its modules shall be collected in one document. These modules are the main
contents of the ETSI-LIB.
This rule is motivated by reasons of maintenance. To maintain several documents is both costly and can
be a source for redundancies and errors.
Rule 5: One module acts as the public interface to the library and this module is called the root. This root
imports and exports every library element defined in any other library module belonging to the library.
The rule is motivated by data encapsulation. The internal structure of the library should neither be known
nor used outside. This gives the LMO the maximum freedom for the internal structure of the library.
5.1.2 Library contents
Rule 6: The library shall only contain validated ASN.1.
The rule is motivated by reasons of correctness. According to the definition of the term "validated ASN.1"
this means that the elements shall comply with ITU-T Recommendation X.680 [2], additionally the
guidance given in ETR 060 [3] shall be followed.
NOTE 1: While the syntactic and semantic correctness according to ASN.1 can be checked by a
tool, it is the responsibility of the LMO to verify that ETR 060 [3] is followed.
Rule 7: The library elements shall be identified as common application elements by the LMO.
The motivation of this rule is to limit the number of elements in the library to only cover the most common
ones. Almost any accepted definition is an investment in the future and it is the LMO's choice to judge
whether a requested definition is likely to be used by more than the requesting standard.

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Rule 8: Every library element shall only be defined once in the library. No library element shall have a
syntactical or semantical duplicate defined elsewhere in the library.
This rule is motivated by reasons of soundness.
NOTE 2: While the syntactical uniqueness can be checked by a tool, it is the responsibility of the
LMO to verify the semantical uniqueness of a library element.
Rule 9: Every library element of type integer, octet string, bit string, character string, sequence of and set
of shall have a reasonable size- or value constraint.
The rule is motivated by implementation and testing limitations. None of them shall be based on error-
prone assumptions on the data size, since there is an elegant way to actually define reasonable
constrains. Guidance on sub-typing is found in ETR 060 [3], subclause 5.4.
Rule 10: If one library element in different versions of the library or different library elements in one
version of the library share a common property, this shared common property shall be expressed in terms
of ASN.1 sub-typing.
This rule ensures, that the interconnection of library elements will be visible. Keeping track of the
relationship to the different library element is a very important factor for the reusability. Without sub-typing
the relationship of two library items might not be obvious, which would exclude potential users from being
notified upon requested changes that might affect them.
In order to achieve a sound library every kind of sub-typing should be applied, including inner sub-typing
and components of. Guidance on sub-typing is found in ETR 060 [3], subclause 5.4.
This rule is motivation by means of type equivalence. An library element including the property of another
library element shall reference that library element by name and not re-define the definition of that library
element, since reusability is the main aim of the library.
Rule 11: A library element shall not re-define a semantical equivalent library element. In such cases
sub-typing or type references shall be used.
Rule 12: The library shall be self-contained. Library elements may only reference other library elements in
the library. No reference to any definition outside the library is allowed.
The motivation of this rule is that the library should not depend on other standards that are subject of
change. A change of the library has to be clear to every user and should never be hidden in some other
document.
5.2 Library index rules
This subclause defines a set of rules applicable to the library index. It is the duty of the LMO to either
apply the rules defined in here or issue a revised version of this TCR-TR.
Rule 13: The library index shall be an ETR, both concerning contents and structure.
The LIB-INDEX will capture the history and relations of events performed upon the library. This
information has no binding impact outside ETSI. However it is significant for maintaining the library over
time. That document was chosen to be an ETR in order to reflect the fact that is will be updated more
often than any other library document.
NOTE: The LMO may later decide to change the LIB-INDEX into an data base application.

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5.2.1 Library index structure
Rule 14: The library index will be paper based.
The rule is motivated by the fact that all ETRs are paper based.
NOTE: An electronic version of the library index may exist in parallel with the paper based
version.
Rule 15: All library index items shall be collected in one document, the LIB-INDEX.
The rule is motivated by reasons of maintenance. To maintain several documents is both costly and can
be a source for redundancies and errors.
5.2.2 Library index contents
Rule 16: The library index shall, for every library element, list the corresponding standards and
recommendations that import this definition (users). Additionally it shall list standards and
recommendations that do not import these definitions but rather define them themselves (definers).
This rule is motivated by the intentions of the library. Without such a list, it is impossible to track down all
parties involved when a change to a library element is requested.
5.3 Library Maintenance Organization (LMO) rules
This subclause defines all rules needed for maintaining and changing the contents of the library as well as
the library index. No administrative procedures are defined.
NOTE: It is possible to extend this TCR-TR with all rules and definitions needed to define the
structure of the LMO as well as its internal administrative behaviour.
It is obvious that a cross-committee group or organization close connected to the ETSI secretariat shall
maintain the library and its index. They have to ensure that the rules and procedures defined here-in are
obeyed executed correctly.
5.3.1 Maintaining the library
Rule 17: The technical responsibility for maintaining the library lies with LMO. The LMO may delegate this
responsibility to any other organization, but it shall keep the overall technical co-ordination and
responsibility of the maintenance.
To have one named organization maintaining the library and the library index will ease the use of the
library as well as clarifying responsibility to the outside world. However, by supporting delegation of
responsibility will not only proclaim the existence of the library, but also link befitting knowledge to the
organization.
Rule 18: Only the LMO shall process the procedures that modify the library.
By delegating the responsibility of maintaining the library, conflicts in performing procedures that modifies
the library may arise between different sub-organizations connected to the LMO. To avoid these conflicts
to happen, only the LMO shall be qualified to performing procedures that modify the library.
5.3.2 Maintaining the library index
Rule 19: Only the LMO shall process the procedures that modify the library index.
By delegating the responsibility of maintaining the library index, conflicts in performing procedures that
modifies the library index may arise between different sub-organizations connected to the LMO. To avoid
these conflicts to happen, only the LMO shall be qualified to performing procedures that modify the library
index.
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5.3.3 Library user support
Rule 20: The use of library elements shall be traceable by updating LIB-INDEX whenever such reference
is requested.
This rule is motivated for capturing the history and relations of events performed to the library.
Rule 21: Whenever an library user makes a reference to some element residing in the library, that
reference has to be made through the public interface as defined in ETSI-LIB. No direct reference to any
specific module residing inside the library is allowed.
As no other possibility exist for referencing library elements, this is the only allowed method. Any other
method is illegal and registers the referencing part as a re-definer of the referenced library element.
5.3.4 Version handling
It is important to have rules for handling different versions of these documents in a proper way.
Rule 22: The responsibility for maintaining the versions falls on the LMO.
As only the LMO may produce new versions of the LIB-R&P, ETSI-LIB and the LIB-INDEX, the LMO shall
be responsible for the version management of these documents.
Rule 23: At a specific moment LIB-R&P, ETSI-LIB and LIB-INDEX shall each have a version number
sequence added to the document title. This dependency is described by adding a version number
sequence to the title of each document as follows:
LIB-R&P Version X;
ETSI-LIB Version X.Y;
LIB-INDEX Version X.Y.Z.
where X, Y and Z are the version numbers of current version of LIB-R&P, ETSI-LIB and LIB-INDEX
respectively.
This rule is motivated by the need of traceability between each documents, which is of great importance.
The soundness of the library index is defined by the library and the correctness of the library is defined by
this TCR-TR. It must thereby be possible to trace this flow of dependency.
The procedural behaviour of updating the different versions is described in clause 7.
6 Procedure definitions
The procedures defined in this TCR-TR are a set of procedures that shall be used to change the library
the library index in terms of contents and structure. No other procedures exist for the library or the library
index. All other procedures needed to support the LMO in its work shall be defined by that LMO.
NOTE: A BNF of the library procedures as well as a procedural semantic definition is given in
annex B.
Rule 24: Every library procedure is addressed to the latest version of the library. No library procedure is
addressed to the library index directly.
This rule clarifies that only one version of the library can exist at a specific moment in time.
In case of inconsistency between the procedure definitions stated below and the procedural semantic
definition is given in annex B, the latter takes precedence.

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6.1 Request
The Request procedure is a procedure targeting the LMO.
Rule 25: The Request procedure shall contain one of the following library procedure:
- register;
- de-register;
- modify;
- remove.
It is the duty of the LMO to execute the library procedure embedded in the Request.
This rule is motivated by the need of executability of a library request. As a library request only can contain
on single library procedure, the execution of that library request will either succeed or fail depending on
the embedded library procedure. If a library request contains more that one library procedure, the
execution result of that library request may be unpredictable.
Rule 26: The result of performing the embedded library procedure shall be returned to the initiator of the
library request.
If a library request modifies the ETSI-LIB, the LIB-INDEX or both, and thereby creates an interim version
of these documents, the final version of that document shall be returned to the initiator of the Request and
not an interim version.
6.1.1 Register
Register is a library procedure that registers the initiator as a user of a library element. If the library
element is not present in the requested version of the library it is added to the library. If the library element
is present in the requested version of the library no change to the library is done. In both cases, the
procedure Register updates the library index with a new library element, the initiator, being a user of the
registered library element.
Rule 27: If a Register library request contains substructure definitions, their registered users shall be the
definition containing the reference to that substructure.
The result of executing the library procedure Register is an interim version of LIB-INDEX with the initiator
of the Register request registered as a user of its request argument, and a possibly interim version of the
ETSI-LIB containing a new library element.
6.1.2 De-register
The procedure De-register de-registers a user of a library element from the LIB-INDEX. The library is
unchanged and an interim version of the LIB-INDEX is produced with the initiator removed as a user of
the library element.
De-register's results are an unchanged ETSI-LIB and an interim version of the LIB-INDEX.
NOTE: If the de-registered user was the last one to use the particular library element, it is up
to the LMO to execute a Remove procedure.

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6.1.3 Modify
Modify is a library procedure that modifies a library element residing in the library. The Modify procedure
can be seen as an execution performed in two steps:
Step 1: Execute library procedure De-register with the original library element as its
argument in order to remove the initiator of the request from the LIB-INDEX as a
user of the library element.
Step 2: Execute library proced
...