ISO/IEC 8825-5:2021

Overview

ISO/IEC 8825-5:2021 specifies a standardized mapping from W3C XML Schema Definitions (XSD) into Abstract Syntax Notation One (ASN.1). The document defines two mapping versions that produce ASN.1 modules and final XER encoding instructions so the resulting ASN.1 schema validates the same set of XML documents and preserves the same semantics as the original XSD. The mapping is intended for use with ASN.1 Extended XML Encoding Rules (EXTENDED‑XER) and enables standardized, vendor‑neutral binary encodings for data originally defined in XSD.

Key topics and requirements

• Two mapping versions: Version 1 and version 2 mappings are specified; both support equivalent semantics and validation coverage for XML documents.
• ASN.1 module generation: Rules for producing ASN.1 type definitions and modules corresponding to XSD constructs (simple types, complex types, elements, attributes, model groups, wildcards).
• XER encoding instructions: The standard specifies the final XER encoding instructions to be applied to ASN.1 types but does not mandate the syntactic form or order of assignment (type‑prefix vs XER Encoding Control Section is left to implementers’ style).
• Preservation of semantics: The mapping ensures the ASN.1 schema and EXTENDED‑XER encodings generate and validate the same XML documents as the original XSD Schema.
• Interoperability with other ASN.1 rules: Other encoding rules (DER, PER, etc.) may be used with the produced ASN.1 types; note that encodings produced by rules such as PER/DER can differ in verbosity and representation (particularly for constructs like dates, times, and wildcards) between mapping versions.
• Support materials: Annexes include ASN.1 type definitions for XSD built‑in types (Annex A & B), examples (Annex D), and guidance on using the mapping for binary transfer of XSD schemas (Annex E).

Applications and who uses it

• Schema translation tools: Implementers building automated XSD→ASN.1 mappers and toolkits.
• Systems requiring compact/canonical encodings: Telecom, IoT, embedded systems, and enterprise integrations that need vendor‑independent binary encodings of XML-defined data.
• Interoperability projects: Organizations that need to reuse existing XSD schemas within ASN.1‑based infrastructures or combine XML toolchains with ASN.1 encoders/decoders.
• Standards bodies and integrators: Working groups defining profiles or protocols that straddle XML and ASN.1 ecosystems.

Related standards

• ISO/IEC 8825 (ASN.1 encoding rules series), including X.690/BER, X.691/PER, and ECN/X.692
• ISO/IEC 8824 (ASN.1 notation and information objects)
• ITU‑T Recommendation X.694 (identical text published as X.694)

Keywords: ISO/IEC 8825-5:2021, ASN.1, XSD to ASN.1 mapping, XER, EXTENDED‑XER, binary encoding, XML Schema, schema translation, ASN.1 modules.