Name: ISO/IEC 13250-4:2009 — Information technology — Topic Maps — Part 4: Canonicalization
SKU: ISO/IEC 13250-4:2009
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Abstract

Overview

ISO/IEC 13250-4:2009 defines Canonical XTM (CXTM) - an XML-based canonicalization format for Topic Maps. CXTM specifies how to transform a Topic Maps Data Model instance (ISO/IEC 13250-2) into an XML Infoset so that semantically equivalent topic maps always produce byte-for-byte identical serializations, and non-equivalent maps produce different serializations. The standard makes topic map equality decidable by simple file comparison and is primarily intended to support portable test suites across Topic Maps implementations.

Key topics and technical requirements

Canonicalization process:
- Input: a Topic Maps Data Model item and a base locator (used to normalize filesystem/URI references).
- Three main steps: produce a CXTM document information item, insert normalized character items/newlines per rules, then serialize using Canonical XML (XML-C14N).
Representation rules:
- Specific mappings from Topic Maps constructs (topicMap, topic, name, variant, occurrence, association, role, scope, itemIdentifiers, subjectLocators, subjectIdentifiers) to XML Infoset element information items.
- Attributes and children order are defined (including representation of reifier, item identifiers, type, value, datatype, and positional/number attributes).
Normalization and ordering:
- Canonical sort order rules determine deterministic ordering of topics, associations, variants, occurrences and locators.
- Locator normalization and string encoding rules (references to Unicode and XML Infoset) to ensure consistent byte-level output.
Interoperability constraints:
- CXTM is designed for testing and comparison, not as the primary interchange format. The standard interchange format remains XTM (ISO/IEC 13250-3).
Normative references include XML Infoset, XML-C14N, RFC 3986 (URI syntax), Unicode, and ISO/IEC 13250-2 (Topic Maps Data Model).

Applications and who should use it

Tool and library developers implementing Topic Maps engines who need deterministic serialization for:
- Automated conformance testing and regression tests.
- Portable test suites across different Topic Maps implementations.
- Verifying equivalence after transformations, merges, or round‑trip processing.
QA engineers, standards testers, and semantic web/knowledge‑management practitioners who require reliable, byte-for-byte comparisons of topic maps.
Not intended as the default interchange format for production data exchange - use XTM (ISO/IEC 13250-3) for interchange.

Related standards

ISO/IEC 13250-2: Topic Maps - Data model (required input model)
ISO/IEC 13250-3: XTM - XML Topic Maps (interchange syntax)
XML Infoset, XML-C14N (Canonical XML), RFC 3986 (URI), Unicode

Keywords: ISO/IEC 13250-4:2009, Canonical XTM, CXTM, Topic Maps, canonicalization, XML Infoset, Canonical XML, topic map canonical serialization, XTM, Topic Maps Data Model.

ISO/IEC 13250-4:2009 PDF

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Abstract

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