Unique Particle Attribution
Encyclopedia
The Unique Particle Attribution (UPA) rule is a mechanism to prevent ambiguity in W3C XML Schema version 1.0.
Due to the UPA rule the XML
schema fragment given below is prohibited:
Given the XML instance fragment:
42
it is ambiguous whether should be associated with the element declaration (xsd:element name="x"), or the wildcard (xsd:any). This ambiguity violates the UPA rule and the corresponding XML schema therefore needs to be rejected by XML schema processors compliant to W3C XML Schema version 1.0.
The W3C XML Schema workgroup is considering so called "weak wildcards" for XML Schema version 1.1. Using weak wildcards, the explicit element declaration would always take precedence over the wildcard, thus removing the ambiguity.
Due to the UPA rule the XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
schema fragment given below is prohibited:
Given the XML instance fragment:
it is ambiguous whether
The W3C XML Schema workgroup is considering so called "weak wildcards" for XML Schema version 1.1. Using weak wildcards, the explicit element declaration would always take precedence over the wildcard, thus removing the ambiguity.
External links
- Article "UPA in plain English"
- Article "Understanding the Unique Particle Attribution Constraint"
- Article "How to set UPA rule violation off"
- XML Schema 1.0: Schema Component Constraint: Unique Particle Attribution
- An Approach for Evolving XML Vocabularies Using XML Schema
- XML Schema 1.1 Part 1: Structures
- XML Schema 1.1 Part 2: Datatypes