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BS ISO IEC 19757 โ Information Technology โ Document Schema Definition Languages (DSDL) Series
Information Technology โ Document Schema Definition Languages (DSDL) (2009โ2016 Editions, 4 Parts)
๐ BS ISO/IEC 19757 is the British Standard implementation, adopted by BSI, of the ISO/IEC 19757 international series prepared by Technical Committee IST/41 (Document description and processing language), classified under ICS 35.240.30. The series standardizes several document validation and description languages under the DSDL (Document Schema Definition Languages) framework, covering rule-based validation (Schematron), extensible datatypes, character repertoire description language (CRDL), and schema association. It is an important standard basis for XML and structured-document validation and interoperability.
๐ก The core idea of DSDL is “multiple complementary schema languages jointly validate a document”: grammar structure (e.g., RELAX NG), rule constraints (Schematron), datatypes, and character-set constraints each have their role, providing more comprehensive validation than a single schema.
1. Series Overview ๐
The BS ISO/IEC 19757 series consists of several parts; this batch covers Parts 3, 5, 7, and 11. Part 3 specifies rule-based validation โ Schematron; Part 5 specifies extensible datatypes; Part 7 specifies the Character Repertoire Description Language (CRDL); Part 11 specifies schema association. Each part is independently complete, addressing different aspects of document validation.
The series primarily serves XML and structured-document standards developers, content management and publishing system developers, designers of e-government and industry data-exchange formats, developers of document validation tools and validation pipelines, and institutions studying data structuring and interoperability.
2. Structure and Technical Highlights ๐
| Standard | Title | Core Content |
|---|---|---|
| BS ISO/IEC 19757-3:2016 | Rule-based validation โ Schematron | Schematron rule language: assertion-based rule validation, abstract patterns, query languages, and report mechanisms; supersedes the 2006 edition |
| BS ISO/IEC 19757-5:2011 | Extensible Datatypes | Datatype constraints in schema definition based on XPath datatypes, including same-named datatypes and simplification rules |
| BS ISO/IEC 19757-7:2009 | Character Repertoire Description Language (CRDL) | Describing the character repertoire and character properties/constraints allowed in a document (scanned version, written from public-domain knowledge) |
| BS ISO/IEC 19757-11:2011 | Schema association | Ways to associate a schema with a document instance: specify the schema used for validation via processing instructions or attributes |
โ ๏ธ BS ISO/IEC 19757-7 in this material is a scanned version; its description is written from public-domain knowledge of the standard. Please refer to the official BSI publication for the authoritative text.
3. Key Technical Requirements ๐ง
The key technical requirements of the BS ISO/IEC 19757 series are reflected in the functional design of each schema language:
- Schematron (Part 3): centered on rules and assertions, expressing constraints with XPath; supports cross-element constraints and context-dependent validation (e.g., “if one element appears, another must appear”).
- Extensible datatypes (Part 5): datatype constraints in schema definition based on XPath datatypes, supporting derived types, same-named datatype reuse, and type simplification, enhancing schema expressiveness.
- Character repertoire description language (Part 7): defines the allowed character repertoire, character properties, and character constraints of a document, for international text and multilingual document validation.
- Schema association (Part 11): specifies how a document instance declares the schema it uses (e.g., via processing instruction or attribute), letting validators automatically locate the schema.
๐จ The expressiveness of schema languages varies: Schematron rule validation and grammar schemas (e.g., RELAX NG) are complementary, not substitutable. A single language often cannot cover all constraints โ adopt the DSDL approach of combining multiple schema languages for layered validation.
4. Engineering Practice Applications ๐ ๏ธ
In engineering practice, the BS ISO/IEC 19757 series is mainly applied to:
- ๐ Industry data-exchange format validation: e-government, publishing, and other industries implement business-rule validation (required fields, inter-field consistency) with Schematron, complementing grammar schemas.
- ๐ง Content management validation pipelines: integrate validation pipelines in CMS and publishing systems, first grammar validation then rule validation, ensuring document quality.
- ๐ Multilingual and international documents: constrain document character repertoire with CRDL, ensuring processability of international documents across language environments.
- ๐ Schema tagging and version management: mark the schema version used in a document instance via the schema association mechanism, enabling compatibility and traceability of schema changes.
โ
It is recommended that document specification developers adopt the DSDL combined-validation approach: constrain structure with RELAX NG or XSD, express business rules with Schematron, and constrain datatypes and character repertoire with datatype languages and CRDL, forming a comprehensive document validation system.
5. Frequently Asked Questions โ
โ Q: What is the difference between Schematron and XML Schema (XSD)?
A: XSD describes document structure (element order, occurrence counts, nesting) โ a grammar schema; Schematron expresses XPath-based assertion rules (cross-field constraints, conditional required fields). They complement and are often used together.
A: XSD describes document structure (element order, occurrence counts, nesting) โ a grammar schema; Schematron expresses XPath-based assertion rules (cross-field constraints, conditional required fields). They complement and are often used together.
โ Q: Why do we need an “extensible datatypes” schema language?
A: Grammar schemas have limited datatype-constraint capability; the extensible datatypes language provides richer type definitions and derivation based on XPath datatypes, letting schemas express more precise data-semantic constraints.
A: Grammar schemas have limited datatype-constraint capability; the extensible datatypes language provides richer type definitions and derivation based on XPath datatypes, letting schemas express more precise data-semantic constraints.
โ Q: How is the Character Repertoire Description Language (CRDL) used in practice?
A: CRDL declares the allowed character repertoire and character properties of a document (e.g., only certain language characters, no control characters), commonly used in multilingual publishing and international data exchange to ensure correct display and processing in target environments.
A: CRDL declares the allowed character repertoire and character properties of a document (e.g., only certain language characters, no control characters), commonly used in multilingual publishing and international data exchange to ensure correct display and processing in target environments.
โ Q: What is the role of “schema association”?
A: Schema association specifies how a document instance declares which schema it uses, avoiding validator guesswork or misconfiguration, simplifying the validation flow and supporting the use of different schema versions for the same document type.
A: Schema association specifies how a document instance declares which schema it uses, avoiding validator guesswork or misconfiguration, simplifying the validation flow and supporting the use of different schema versions for the same document type.
โ Q: Are the parts of BS ISO/IEC 19757 independent?
A: Yes. Under the DSDL framework, each part is independently complete and can be used alone or in combination. An organization can select only the parts it needs without implementing the entire series.
A: Yes. Under the DSDL framework, each part is independently complete and can be used alone or in combination. An organization can select only the parts it needs without implementing the entire series.