View source for Value arithmetic required - elements

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= Value arithmetic required - elements (a co-constraint use case) =

Require the values of specified children to satisfy an equation
or an inequality.

Cf. [[Value arithmetic required - attributes]], which formulates a similar
use case involving attributes (and an inequality).

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

source: Margrethe Fossberg
[http://lists.w3.org/Archives/Public/xmlschema-dev/2001Sep/0036.html]

== Description ==

    I would like, say, elements a, b, and c to have a min
    value of 0 and max value of 15, but the total sum of a, b and c cannot
    exceed 30.  Is this possible at all?

== Analysis ==

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

== Possible solutions ==

=== Relax NG ===
=== Schematron ===
=== Check clause ===
If the elements ''a'', ''b'', ''c'' are siblings, then 
a simple check clause on the parent will do:

<pre><nowiki>
 <xsd:simpleType name="max15">
  <xsd:restriction base="xsd:decimal">
   <xsd:minInclusive value="0.0"/>
   <xsd:maxInclusive value="15.0">
   </xsd:maxInclusive>
  </xsd:restriction>
 </xsd:simpleType>
 <xsd:element name="container">
  <xsd:complexType>
   <xsd:annotation><xsd:appinfo><sch:pattern><sch:rule>
       <sch:assert test="(./a + ./b + ./c) &lt;= 30">
	The sum of a, b, and c must not exceed 30.
       </sch:assert>
      </sch:rule></sch:pattern></xsd:appinfo></xsd:annotation>
   <xsd:sequence>
    <xsd:element name="a" type="this:max15"/>
    <xsd:element name="b" type="this:max15"/>
    <xsd:element name="c" type="this:max15"/>
   </xsd:sequence>
  </xsd:complexType>
 </xsd:element>
</nowiki></pre>

=== [[SchemaPath]] ===
If ''T'' is the name of the type assigned under normal circumstances to the
container element, then we can write 

<pre><nowiki>
<xsd:element name="container">
  <xsd:alt cond="./a + ./b + ./c > 30.00" type="xsd:error"/>
  <xsd:alt type="T"/>
</xsd:element>
</nowiki></pre>

=== Conditional Type ===

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[[Category:CoConstraintUseCase]]