ISO/IEC 8824-4:2021

INTERNATIONAL ISO/IEC
STANDARD 8824-4
Sixth edition
2021-06
Information technology — Abstract
Syntax Notation One (ASN.1) —
Part 4:
Parameterization of ASN.1
specifications
Technologies de l'information — Notation de syntaxe abstraite
numéro un (ASN.1) —
Partie 4: Paramétrage des spécifications de la notation de syntaxe
abstraite numéro un
Reference number
ISO/IEC 8824-4:2021(E)
©
ISO/IEC 2021

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ISO/IEC 8824-4:2021(E)

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ISO/IEC 8824-4:2021(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
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Attention is drawn to the possibility that some of the elements of this document may be the subject of
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of any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC list of patent
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For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
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see www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 6, Telecommunications and information exchange between systems, in collaboration
with ITU-T. The identical text is published as ITU-T X.683 (02/2021).
This sixth edition cancels and replaces the fifth edition (ISO/IEC 8824-4:2015), which has been
technically revised. It also incorporates ISO/IEC 8824-4:2015/Cor 1:2018.
A list of all parts in the ISO/IEC 8824 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html and www.iec.ch/national-
committees.
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ISO/IEC 8824-4:2021(E)
CONTENTS
Page
Introduction . iv
1 Scope . 1
2 Normative references . 1
2.1 Identical Recommendations | International Standards . 1
3 Definitions . 1
3.1 Specification of basic notation . 1
3.2 Information object specification . 1
3.3 Constraint specification . 1
3.4 Additional definitions . 1
4 Abbreviations . 2
5 Convention . 2
6 Notation . 2
6.1 Assignments . 2
6.2 Parameterized definitions . 2
6.3 Symbols . 3
7 ASN.1 lexical items . 3
8 Parameterized assignments . 3
9 Referencing parameterized definitions . 5
10 Abstract syntax parameters . 7
Annex A – Examples . 9
A.1 Example of the use of a parameterized type definition . 9
A.2 Example of use of parameterized definitions together with an information object class . 9
A.3 Example of parameterized type definition that is finite . 10
A.4 Example of a parameterized value definition . 11
A.5 Example of a parameterized value set definition. 11
A.6 Example of a parameterized class definition . 11
A.7 Example of a parameterized object set definition . 12
A.8 Example of a parameterized object set definition . 12
Annex B – Summary of the notation . 13

 Rec. ITU-T X.683 (02/2021) iii
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ISO/IEC 8824-4:2021(E)
Introduction
Application designers need to write specifications in which certain aspects are left undefined. Those aspects will later be
defined by one or more other groups (each in its own way), to produce a fully defined specification for use in the definition
of an abstract syntax (one for each group).
In some cases, aspects of the specification (for example, bounds) may be left undefined even at the time of abstract syntax
definition, being completed by the specification of International Standardized Profiles or functional profiles from some
other body.
NOTE 1 – It is a requirement imposed by this Recommendation | International Standard that any aspect that is not solely concerned
with the application of constraints has to be completed prior to the definition of an abstract syntax.
In the extreme case, some aspects of the specification may be left for the implementer to complete, and would then be
specified as part of the Protocol Implementation Conformance Statement.
While the provisions of Rec. ITU-T X.681 | ISO/IEC 8824-2 and Rec. ITU-T X.682 | ISO/IEC 8824-3 provide a
framework for the later completion of parts of a specification, they do not of themselves solve the above requirements.
Additionally, a single designer sometimes requires to define many types, or many information object classes, or many
information object sets, or many information objects, or many values, which have the same outer level structure, but differ
in the types, or information object classes, or information object sets, or information objects, or values, that are used at
an inner level. Instead of writing out the outer level structure for every such occurrence, it is useful to be able to write it
out once, with parts left to be defined later, then to refer to it and provide the additional information.
All these requirements are met by the provision for parameterized reference names and parameterized assignments by
this Recommendation | International Standard.
The syntactic form of a parameterized reference name is the same as that of the corresponding normal reference name,
but the following additional considerations apply:
– When it is assigned in a parameterized assignment statement, it is followed by a list of dummy reference
names in braces, each possibly accompanied by a governor; these reference names have a scope which is
the right-hand side of the assignment statement, and the parameter list itself.
NOTE 2 – This is what causes it to be recognized as a parameterized reference name.
– When it is exported or imported, it is followed by a pair of empty braces to distinguish it as a parameterized
reference name.
– When it is used in any construct, it is followed by a list of syntactic constructions, one for each dummy
reference name, that provide an assignment to the dummy reference name for the purposes of that use only.
Dummy reference names have the same syntactic form as the corresponding normal reference name, and can be used
anywhere on the right-hand side of the assignment statement that the corresponding normal reference name could be used.
All such usages are required to be consistent.

iv Rec. ITU-T X.683 (02/2021)
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ISO/IEC 8824-4:2021 (E)
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION
Information Technology – Abstract Syntax Notation ONE (ASN.1):
Parameterization of ASN.1 specifications
1 Scope
This Recommendation | International Standard is part of Abstract Syntax Notation One (ASN.1) and defines notation for
parameterization of ASN.1 specifications.
2 Normative references
The following Recommendations and International Standards contain provisions which, through reference in this text,
constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated
were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this
Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent edition
of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid
International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid
ITU-T Recommendations.
2.1 Identical Recommendations | International Standards
– Recommendation ITU-T X.680 (2021) | ISO/IEC 8824-1:2021, Information technology – Abstract Syntax
Notation One (ASN.1): Specification of basic notation.
– Recommendation ITU-T X.681 (2021) | ISO/IEC 8824-2:2021, Information technology – Abstract Syntax
Notation One (ASN.1): Information object specification.
– Recommendation ITU-T X.682 (2021) | ISO/IEC 8824-3:2021, Information technology – Abstract Syntax
Notation One (ASN.1): Constraint specification.
NOTE – The references above shall be interpreted as references to the identified Recommendations | International Standards
together with all their published amendments and technical corrigenda.
3 Definitions
For the purposes of this Recommendation | International Standard, the following definitions apply.
3.1 Specification of basic notation
This Recommendation | International Standard uses the terms defined in Rec. ITU-T X.680 | ISO/IEC 8824-1.
3.2 Information object specification
This Recommendation | International Standard uses the terms defined in Rec. ITU-T X.681 | ISO/IEC 8824-2.
3.3 Constraint specification
This Recommendation | International Standard uses the terms defined in Rec. ITU-T X.682 | ISO/IEC 8824-3.
3.4 Additional definitions
3.4.1 normal reference name: A reference name defined, without parameters, by means of an "Assignment" other
than a "ParameterizedAssignment". Such a name references a complete definition and is not supplied with actual
parameters when used.
3.4.2 parameterized reference name: A reference name defined using a parameterized assignment, which
references an incomplete definition and which, therefore, must be supplied with actual parameters when used.
3.4.3 parameterized type: A type defined using a parameterized type assignment and thus whose components are
incomplete definitions which must be supplied with actual parameters when the type is used.
 Rec. ITU-T X.683 (02/2021) 1
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ISO/IEC 8824-4:2021 (E)
3.4.4 parameterized value: A value defined using a parameterized value assignment and thus whose value is
incompletely specified and must be supplied with actual parameters when used.
3.4.5 parameterized value set: A value set defined using a parameterized value set assignment and thus whose
values are incompletely specified and must be supplied with actual parameters when used.
3.4.6 parameterized object class: An information object class defined using a parameterized object class assignment
and thus whose field specifications are incompletely specified and must be supplied with actual parameters when used.
3.4.7 parameterized object: An information object defined using a parameterized object assignment and thus whose
components are incompletely specified and must be supplied with actual parameters when used.
3.4.8 parameterized object set: An information object set defined using a parameterized object set assignment and
thus whose objects are incompletely specified and must be supplied with actual parameters when used.
3.4.9 variable constraint: A constraint employed in specifying a parameterized abstract syntax, and which depends
on some parameter of the abstract syntax.
4 Abbreviations
For the purposes of this Recommendation | International Standard, the following abbreviation applies:
ASN.1 Abstract Syntax Notation One
5 Convention
This Recommendation | International Standard employs the notational convention defined in Rec. ITU-T X.680 |
ISO/IEC 8824-1, clause 5.
6 Notation
This clause summarizes the notation defined in this Recommendation | International Standard.
6.1 Assignments
The following notation which can be used as an alternative for "Assignment" (see Rec. ITU-T X.680 | ISO/IEC 8824-1,
clause 13) is defined in this Recommendation | International Standard:
– ParameterizedAssignment (see 8.1).
6.2 Parameterized definitions
6.2.1 The following notation which can be used as an alternative for "DefinedType" (see Rec. ITU-T X.680 |
ISO/IEC 8824-1, 14.1) is defined in this Recommendation | International Standard:
– ParameterizedType (see 9.2).
6.2.2 The following notation which can be used as an alternative for "DefinedValue" (see Rec. ITU-T X.680 |
ISO/IEC 8824-1, 14.1) is defined in this Recommendation | International Standard:
– ParameterizedValue (see 9.2).
6.2.3 The following notation which can be used as an alternative for "DefinedType" (see Rec. ITU-T X.680 |
ISO/IEC 8824-1, 14.1) is defined in this Recommendation | International Standard:
– ParameterizedValueSetType (see 9.2).
6.2.4 The following notation which can be used as an alternative for "ObjectClass" (see Rec. ITU-T X.681 |
ISO/IEC 8824-2, 9.2) is defined in this Recommendation | International Standard:
– ParameterizedObjectClass (see 9.2).
6.2.5 The following notation which can be used as an alternative for "Object" (see Rec. ITU-T X.681 | ISO/IEC 8824-
2, 11.3) is defined in this Recommendation | International Standard:
– ParameterizedObject (see 9.2).
6.2.6 The following notation which can be used as an alternative for "ObjectSet" (see Rec. ITU-T X.681 |
ISO/IEC 8824-2, 12.3) is defined in this Recommendation | International Standard:
2 Rec. ITU-T X.683 (02/2021)
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ISO/IEC 8824-4:2021 (E)
– ParameterizedObjectSet (see 9.2).
6.3 Symbols
The following notation which can be used as an alternative for "Symbol" (see Rec. ITU-T X.680 | ISO/IEC 8824-1, 13.1)
is defined in this Recommendation | International Standard:
– ParameterizedReference (see 9.1).
7 ASN.1 lexical items
This Recommendation | International Standard makes use of the lexical items specified in Rec. ITU-T X.680 |
ISO/IEC 8824-1, clause 12.
8 Parameterized assignments
8.1 There are parameterized assignment statements corresponding to each of the assignment statements specified
in Rec. ITU-T X.680 | ISO/IEC 8824-1 and Rec. ITU-T X.681 | ISO/IEC 8824-2. The "ParameterizedAssignment"
construct is:
ParameterizedAssignment ::=
ParameterizedTypeAssignment
| ParameterizedValueAssignment
| ParameterizedValueSetTypeAssignment
| ParameterizedObjectClassAssignment
| ParameterizedObjectAssignment
| ParameterizedObjectSetAssignment
8.2 Each "ParameterizedAssignment" has the same syntax as "Assignment" except that following the
initial lexical item there is a "ParameterList". The initial item thereby becomes a parameterized reference name
(see 3.4.2):
NOTE 1 – Rec. ITU-T X.680 | ISO/IEC 8824-1 imposes the requirement that all reference names assigned within a module, whether
parameterized or not, must be distinct.
NOTE 2 – Where value notation is governed by a parameterized type (or a type that is a parameter) the validity of value notation
within the parameterized assignment can only be determined after instantiation of the parameterized type, and may be valid for
some instantiations and invalid for others.
ParameterizedTypeAssignment ::=
typereference
ParameterList
"::="
Type
ParameterizedValueAssignment ::=
valuereference
ParameterList
Type
"::="
Value
ParameterizedValueSetTypeAssignment ::=
typereference
ParameterList
Type
"::="
ValueSet
ParameterizedObjectClassAssignment ::=
objectclassreference
ParameterList
"::="
ObjectClass
ParameterizedObjectAssignment ::=
objectreference
 Rec. ITU-T X.683 (02/2021) 3
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ISO/IEC 8824-4:2021 (E)
ParameterList
DefinedObjectClass
"::="
Object
ParameterizedObjectSetAssignment ::=
objectsetreference
ParameterList
DefinedObjectClass
"::="
ObjectSet
8.3 A "ParameterList" is a list of "Parameter"s between braces:
ParameterList ::= "{" Parameter "," + "}"
Each "Parameter" consists of a "DummyReference" and possibly a "ParamGovernor":
Parameter ::= ParamGovernor ":" DummyReference | DummyReference
ParamGovernor ::= Governor | DummyGovernor
Governor ::= Type | DefinedObjectClass
DummyGovernor ::= DummyReference
DummyReference ::= Reference
A "DummyReference" in "Parameter" may stand for:
a) a "Type" or "DefinedObjectClass", in which case there shall be no "ParamGovernor";
b) a "Value" or "ValueSet", in which case the "ParamGovernor" shall be present, and in case
"ParamGovernor" is a "Governor" it shall be a "Type", and in case "ParamGovernor" is a
"DummyGovernor" the actual parameter for the "ParamGovernor" shall be a "Type";
c) an "Object" or "ObjectSet", in which case the "ParamGovernor" shall be present, and in case
"ParamGovernor" is a "Governor" it shall be a "DefinedObjectClass", and in case "ParamGovernor" is a
"DummyGovernor" the actual parameter for the "ParamGovernor" shall be a "DefinedObjectClass".
A "DummyGovernor" shall be a "DummyReference" that has no "Governor".
8.4 The scope of a "DummyReference" appearing in a "ParameterList" is the "ParameterList" itself, together with
that part of the "ParameterizedAssignment" which follows the "ParameterList". The "DummyReference" hides any other
"Reference" with the same name in that scope in any given instantiation.
NOTE – This subclause does not apply to "identifier"s defined in "NamedNumberList"s, "Enumeration"s and "NamedBitList"s,
since they are not "Reference"s. The "DummyReference" does not hide these "identifier"s (see Rec. ITU-T X.680 | ISO/IEC
8824-1, 19.12 and 20.11).
8.5 The usage of a "DummyReference" within its scope shall be consistent with its syntactic form, and, where
applicable, governor, and all usages of the same "DummyReference" shall be consistent with one another.
NOTE – Where the syntactic form of a dummy reference name is ambiguous (for example, between whether it is an
"objectclassreference" or "typereference"), the ambiguity can normally be resolved on the first use of the dummy reference name
on the right-hand side of the assignment statement. Thereafter, the nature of the dummy reference name is known. The nature of
the dummy reference is, however, not determined solely by the right-hand side of the assignment statement when it is in turn used
only as an actual parameter in a parameterized reference; in this case, the nature of the dummy reference must be determined by
examining the definition of this parameterized reference. Users of the notation are warned that such a practice can make ASN.1
specifications less clear, and it is suggested that adequate comments are provided to explain this for human readers.
Example
Consider the following parameterized object class assignment:
PARAMETERIZED-OBJECT-CLASS { TypeParam, INTEGER:valueParam, INTEGER:ValueSetParam } ::=
CLASS {
&valueField1 TypeParam,
&valueField2 INTEGER DEFAULT valueParam,
&valueField3 INTEGER (ValueSetParam),
&ValueSetField INTEGER DEFAULT { ValueSetParam }
}
For the purpose of determining proper usage of the "DummyReference"s in the scope of the "Parameterized Assignment",
and for that purpose only, the "DummyReference"s can be regarded to be defined as follows:
4 Rec. ITU-T X.683 (02/2021)
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TypeParam ::= UnspecifiedType
valueParam INTEGER ::= unspecifiedIntegerValue
ValueSetParam INTEGER ::= { UnspecifiedIntegerValueSet }
where:
a) TypeParam is a "DummyReference" which stands for a "Type". Therefore TypeParam can be used
wherever a "typereference" can be used, e.g. as a "Type" for the fixed-type value field valueField1.
b) valueParam is a "DummyReference" which stands for a value of an integer type. Therefore valueParam
can be used wherever a "valuereference" of an integer value can be used, e.g. as a default value for the
fixed-type value field valueField2.
c) ValueSetParam is a "DummyReference" which stands for a value set of an integer type. Therefore
ValueSetParam can be used wherever a "typereference" of an integer value can be used, e.g. as a "Type"
in the "ContainedSubtype" notation for valueField3 and ValueSetField.
8.6 Each "DummyReference" shall be employed at least once within its scope.
NOTE – If the "DummyReference" did not so appear, then the corresponding "ActualParameter" would have no effect on the
definition, and would simply be "discarded", while to the user it might seem that some specification was taking place.
"ParameterizedValueAssignment"s, "ParameterizedValueSetTypeAssignment"s, "ParameterizedObjectAssignment"s
and "ParameterizedObjectSetAssignment"s that contain either a direct or indirect reference to themselves are illegal.
8.7 Given a set of parameterized assignments (one or more) and a recursive path of parameterized references
crossing one or more of those parameterized assignments, all the parameterized references along that path shall satisfy
the following condition: Each actual parameter present in the parameterized reference shall either consist solely of a
dummy reference (with no lexical items or comments preceding or following the dummy reference) or shall not contain
any dummy reference (see A.3).
8.8 In the definition of a "ParameterizedType", "ParameterizedValueSet", or "ParameterizedObjectClass", a
circular reference to the item being defined shall not be made, unless such reference is directly or indirectly marked
OPTIONAL or, in the case of "ParameterizedType" and "ParameterizedValueSet", made through a reference to a choice
type, at least one of whose alternatives is non-circular in definition.
8.9 The governor of a "DummyReference" shall not include a reference to another "DummyReference" if that other
"DummyReference" also has a governor.
8.10 In a parameterized assignment the right side of the "::=" shall not consist solely of a "DummyReference".
8.11 The governor of a "DummyReference" shall not require knowledge of either the "DummyReference" or of the
parameterized reference name being defined.
8.12 When a value or value set is supplied to a parameterized type as an actual parameter, the type of the actual
parameter is required to be compatible with the governor of the corresponding dummy parameter. (See Rec. ITU-T X.680
| ISO/IEC 8824-1, C.6.2 and C.6.3 for details.)
8.13 In defining a parameterized type with a value or a value set dummy parameter, the type used to govern that
dummy parameter shall be a type, all of whose values are valid for use in all places to the right of the assignment where
the dummy parameter is used. (See Rec. ITU-T X.680 | ISO/IEC 8824-1, C.6.5 for details.)
9 Referencing parameterized definitions
9.1 Within a "SymbolList" (in "Exports" or "Imports") a parameterized definition shall be referenced by a
"ParameterizedReference":
ParameterizedReference ::= Reference | Reference "{" "}"
where "Reference" is the first lexical item in the "ParameterizedAssignment", as specified in 8.2 above.
NOTE – The first alternative of "ParameterizedReference" is provided solely as an aid to human understanding. Both alternatives
have the same meaning.
9.2 Other than in "Exports" or "Imports", a parameterized definition shall be referenced by a "Parameterized"
construct, which can be used as an alternative for the corresponding "":
ParameterizedType ::=
SimpleDefinedType
ActualParameterList
 Rec. ITU-T X.683 (02/2021) 5
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ISO/IEC 8824-4:2021 (E)
SimpleDefinedType ::=
ExternalTypeReference |
typereference
ParameterizedValue ::=
SimpleDefinedValue
ActualParameterList
SimpleDefinedValue ::=
ExternalValueReference |
valuereference
ParameterizedValueSetType ::=
SimpleDefinedType
ActualParameterList
ParameterizedObjectClass ::=
DefinedObjectClass
ActualParameterList
ParameterizedObjectSet ::=
DefinedObjectSet
ActualParameterList
ParameterizedObject ::=
DefinedObject
ActualParameterList
9.3 The reference name in the "Defined" shall be a reference name to which an assignment is made in a
"ParameterizedAssignment".
9.4 The restrictions on the "Defined" alternative to be used, which are specified in Rec. ITU-T X.680 |
ISO/IEC 8824-1 and Rec. ITU-T X.681 | ISO/IEC 8824-2 as normal reference names, apply equally to the corresponding
parameterized reference names.
NOTE – In essence, the restrictions are as follows: each "Defined" has two alternatives, "reference" and
"ExternalReference". The former is used within the module of definition or if the definition has been imported and there is no
name conflict; the latter is used where there is no imports listed (deprecated), or if there is a conflict between the imported name
...