View source for Value equality - and null/non-null

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= Value equality (a co-constraint use case) =

Make the required/optional (or nillable/non-nillable?) property of
a child element (or attribute?) depend on the values of one or more
other elements or attributes.

source: Frank Langel
[http://lists.w3.org/Archives/Public/xmlschema-dev/2002Aug/0051.html]

(See also [[Value equality - and following siblings]] and
[[Value equality - and children of following sibling]].

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Other use cases: [[Co-constraint Use Cases]]

== Description ==

    a validation rule such as "if field a==21 and b==32 and field x==field z
    then c must be not null"

== Analysis ==

(Add your analysis here; see your name in pixels!)

== Possible solutions ==

=== Relax NG ===
=== Schematron ===
=== Check clause ===
=== [[SchemaPath]] ===
=== Conditional Type ===

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[[Category:CoConstraintUseCase]]