ISO/IEC 8825-5:2021

INTERNATIONAL ISO/IEC
STANDARD 8825-5
Fourth edition
2021-06
Information technology — ASN.1
encoding rules —
Part 5:
Mapping W3C XML schema definitions
into ASN.1
Technologies de l'information — Règles de codage ASN.1 —
Partie 5: Mappage en ASN.1 des définitions de schéma XML du W3C
Reference number
©
ISO/IEC 2021
© ISO/IEC 2021
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ii © ISO/IEC 2021 – All rights reserved

Foreword
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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.694 (02/2021).
This fourth edition cancels and replaces the third edition (ISO/IEC 8825-5:2015), which has been
technically revised.
A list of all parts in the ISO/IEC 8825 series can be found on the ISO and IEC websites.
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© ISO/IEC 2021 – All rights reserved iii

CONTENTS
Page
1 Scope . 1
2 Normative references. 1
2.1 Identical Recommendations | International Standards . 1
2.2 Additional references . 2
3 Definitions . 2
3.1 Imported definitions . 2
3.2 Additional definitions . 3
4 Abbreviations . 3
5 Notation . 3
6 Purpose and extent of standardization . 3
7 Mapping XSD Schemas . 4
8 Ignored schema components and properties . 5
9 ASN.1 modules . 6
10 Name conversion . 6
10.1 General . 6
10.2 Generating ASN.1 type definitions that are references to ASN.1 type assignments . 7
10.3 Generating identifiers and type reference names . 7
10.4 Order of the mapping . 9
11 Mapping uses of XSD built-in types . 10
12 Mapping facets. 10
12.1 The length, minLength, and maxLength facets . 11
12.2 The pattern facet . 11
12.3 The whiteSpace facet. 11
12.4 The enumeration facet . 12
12.5 Other facets . 14
13 Mapping simple type definitions . 14
14 Mapping element declarations . 16
15 Mapping attribute declarations . 17
16 Mapping values of simple type definitions . 17
17 Mapping model group definitions . 17
18 Mapping model groups . 17
19 Mapping particles . 18
20 Mapping complex type definitions. 19
21 Mapping wildcards . 20
22 Mapping attribute uses . 22
23 Mapping uses of simple and complex type definitions (general case) . 22
24 Mapping special uses of simple and complex type definitions (substitutable) . 23
25 Mapping special uses of simple and complex type definitions (substitutable, nillable) . 24
26 Mapping special uses of simple type definitions (nillable) . 25
27 Mapping special uses of complex type definitions (nillable) . 26
28 Mapping special uses of element declarations (head of element substitution group) . 27
29 Generating special ASN.1 type assignments for types used in element declarations . 27
30 Generating special ASN.1 type assignments for types belonging to a derivation hierarchy . 29
31 Generating special ASN.1 type assignments for element substitution groups . 29
Annex A – ASN.1 type definitions corresponding to XSD built-in types for the version 1 mapping . 30
Annex B – ASN.1 type definitions corresponding to XSD built-in types for the version 2 mapping . 33
Rec. ITU-T X.694 (02/2021) iii
© ISO/IEC 2021 – All rights reserved

Page
Annex C – Identification of the XSD module. 37
Annex D – Examples of mappings . 38
D.1 A Schema using simple type definitions . 38
D.2 The corresponding ASN.1 definitions . 39
D.3 Further examples . 40
Annex E – Use of the mapping to provide binary encodings for W3C XML Schema . 60
E.1 Encoding XSD Schemas . 60
E.2 Transfer without using the XSD Schema for Schemas . 60
E.3 Transfer using the XSD Schema for Schemas . 60

iv Rec. ITU-T X.694 (02/2021)
© ISO/IEC 2021 – All rights reserved

Introduction
This Recommendation | International Standard specifies version 1 and version 2 of a mapping from a W3C XML Schema
definition (an XSD Schema) into an Abstract Syntax Notation One (ASN.1) schema. The mappings can be applied to any
XSD Schema. Both mappings specify the generation of one or more ASN.1 modules containing type definitions, together
with ASN.1 XER encoding instructions. These are jointly described as an ASN.1 schema for Extensible Markup Language
(XML) documents. This ASN.1 schema (produced by either version of the mapping), when used with the ASN.1 Extended
XML Encoding Rules (EXTENDED-XER), can be used to generate and to validate the same set of W3C XML 1.0
documents as the original XSD Schema. The resulting ASN.1 types and encodings support the same semantic content as
the XSD Schema. Thus ASN.1 tools can be used interchangeably with XSD tools for the generation and processing of
the specified XML documents.
Other standardized ASN.1 encoding rules, such as the Distinguished Encoding Rules (DER) or the Packed Encoding
Rules (PER), can be used in conjunction with this standardized mapping, but produce encodings for version 2 of the
mapping that differ from (and are less verbose than) those produced by version 1 for XSD constructs involving dates and
times or wildcards.
The combination of this Recommendation | International Standard with ASN.1 Encoding Rules provides fully
standardized and vendor-independent compact and canonical binary encodings for data originally defined using an XSD
Schema.
The ASN.1 schema provides a clear separation between the specification of the information content of messages
(their abstract syntax) and the precise form of the XML document (e.g., use of attributes instead of elements). This results
in both a clearer and generally a less verbose schema than the original XSD Schema.
Annex A forms an integral part of this Recommendation | International Standard, and is an ASN.1 module containing a
set of ASN.1 type assignments that correspond to each of the XSD built-in types for version 1 of the mapping. Mappings
of XSD Schemas into ASN.1 schemas either import the type reference names of those type assignments or include the
type definitions in-line.
Annex B also forms an integral part of this Recommendation | International Standard and provides the ASN.1 module for
version 2 of the mapping.
Annex C does not form an integral part of this Recommendation | Intern
...