[xml] XSD - how to allow elements in any order any number of times?

I am trying to create an XSD, and trying to write the definition with the following requirement:

• Allow child element specified to appear any number of times (0 to unbounded)
• Allow child elements to be in any order

I looked around and found various solutions like this:

<xs:element name="foo">
  <xsl:complexType>
    <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="child1" type="xs:int"/>
      <xs:element name="child2" type="xs:string"/>
    </xs:choice>
  </xs:complexType>
</xs:element>

But from what I understand xs:choice still only allows single element selection. Hence setting the MaxOccurs to unbounded like this should only mean that "any one" of the child elements can appear multiple times. Is this accurate?

If above solution is incorrect, how can I achieve what I stated above in my requirement?

EDIT: What if the requirement is as follows?

• Element child1 child2 can appear any number of times (0 to unbounded)
• Elements to be in any order
• Elements child3 and child4 should appear exactly once.

For example, this xml is valid:

<foo>
<child1> value </child1>
<child1> value </child1>
<child3> value </child3>
<child2> value </child2>
<child4> value </child4>
<child1> value </child1>
</foo>

but this is not (missing child3)

<foo>
<child1> value </child1>
<child1> value </child1>
<child2> value </child2>
<child4> value </child4>
<child1> value </child1>
</foo>

You should find that the following schema allows the what you have proposed.

  <xs:element name="foo">
    <xs:complexType>
      <xs:sequence minOccurs="0" maxOccurs="unbounded">
        <xs:choice>
          <xs:element maxOccurs="unbounded" name="child1" type="xs:unsignedByte" />
          <xs:element maxOccurs="unbounded" name="child2" type="xs:string" />
        </xs:choice>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

This will allow you to create a file such as:

<?xml version="1.0" encoding="utf-8" ?>
<foo>
  <child1>2</child1>
  <child1>3</child1>
  <child2>test</child2>
  <child2>another-test</child2>
</foo>

Which seems to match your question.

This is what finally worked for me:

<xsd:element name="bar">
  <xsd:complexType>
    <xsd:sequence>
      <!--  Permit any of these tags in any order in any number     -->
      <xsd:choice minOccurs="0" maxOccurs="unbounded">
        <xsd:element name="child1" type="xsd:string" />
        <xsd:element name="child2" type="xsd:string" />
        <xsd:element name="child3" type="xsd:string" />
      </xsd:choice>
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>

The alternative formulation of the question added in a later edit seems still to be unanswered: how to specify that among the children of an element, there must be one named child3, one named child4, and any number named child1 or child2, with no constraint on the order in which the children appear.

This is a straightforwardly definable regular language, and the content model you need is isomorphic to a regular expression defining the set of strings in which the digits '3' and '4' each occur exactly once, and the digits '1' and '2' occur any number of times. If it's not obvious how to write this, it may help to think about what kind of finite state machine you would build to recognize such a language. It would have at least four distinct states:

• an initial state in which neither '3' nor '4' has been seen
• an intermediate state in which '3' has been seen but not '4'
• an intermediate state in which '4' has been seen but not '3'
• a final state in which both '3' and '4' have been seen

No matter what state the automaton is in, '1' and '2' may be read; they do not change the machine's state. In the initial state, '3' or '4' will also be accepted; in the intermediate states, only '4' or '3' is accepted; in the final state, neither '3' nor '4' is accepted. The structure of the regular expression is easiest to understand if we first define a regex for the subset of our language in which only '3' and '4' occur:

(34)|(43)

To allow '1' or '2' to occur any number of times at a given location, we can insert (1|2)* (or [12]* if our regex language accepts that notation). Inserting this expression at all available locations, we get

(1|2)*((3(1|2)*4)|(4(1|2)*3))(1|2)*

Translating this into a content model is straightforward. The basic structure is equivalent to the regex (34)|(43):

<xsd:complexType name="paul0">
  <xsd:choice>
    <xsd:sequence>
      <xsd:element ref="child3"/>
      <xsd:element ref="child4"/>
    </xsd:sequence>
    <xsd:sequence>
      <xsd:element ref="child4"/>
      <xsd:element ref="child3"/>
    </xsd:sequence>
  </xsd:choice>
</xsd:complexType>

Inserting a zero-or-more choice of child1 and child2 is straightforward:

<xsd:complexType name="paul1">
  <xsd:sequence>
    <xsd:choice minOccurs="0" maxOccurs="unbounded">
      <xsd:element ref="child1"/>
      <xsd:element ref="child2"/>
    </xsd:choice>      
    <xsd:choice>
      <xsd:sequence>
        <xsd:element ref="child3"/>
        <xsd:choice minOccurs="0" maxOccurs="unbounded">
          <xsd:element ref="child1"/>
          <xsd:element ref="child2"/>
        </xsd:choice>      
        <xsd:element ref="child4"/>
      </xsd:sequence>
      <xsd:sequence>
        <xsd:element ref="child4"/>
        <xsd:choice minOccurs="0" maxOccurs="unbounded">
          <xsd:element ref="child1"/>
          <xsd:element ref="child2"/>
        </xsd:choice>      
        <xsd:element ref="child3"/>
      </xsd:sequence>
    </xsd:choice>
    <xsd:choice minOccurs="0" maxOccurs="unbounded">
      <xsd:element ref="child1"/>
      <xsd:element ref="child2"/>
    </xsd:choice>      
  </xsd:sequence>
</xsd:complexType>

If we want to minimize the bulk a bit, we can define a named group for the repeating choices of child1 and child2:

<xsd:group name="onetwo">
  <xsd:choice>
    <xsd:element ref="child1"/>
    <xsd:element ref="child2"/>
  </xsd:choice>   
</xsd:group>

<xsd:complexType name="paul2">
  <xsd:sequence>
    <xsd:group ref="onetwo" minOccurs="0" maxOccurs="unbounded"/>
    <xsd:choice>
      <xsd:sequence>
        <xsd:element ref="child3"/>
        <xsd:group ref="onetwo" minOccurs="0" maxOccurs="unbounded"/>
        <xsd:element ref="child4"/>
      </xsd:sequence>
      <xsd:sequence>
        <xsd:element ref="child4"/>
        <xsd:group ref="onetwo" minOccurs="0" maxOccurs="unbounded"/>
        <xsd:element ref="child3"/>
      </xsd:sequence>
    </xsd:choice>  
    <xsd:group ref="onetwo" minOccurs="0" maxOccurs="unbounded"/>
  </xsd:sequence>
</xsd:complexType>

In XSD 1.1, some of the constraints on all-groups have been lifted, so it's possible to define this content model more concisely:

<xsd:complexType name="paul3">
  <xsd:all>
    <xsd:element ref="child1" minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element ref="child2" minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element ref="child3"/>
    <xsd:element ref="child4"/>      
  </xsd:all>
</xsd:complexType>

But as can be seen from the examples given earlier, these changes to all-groups do not in fact change the expressive power of the language; they only make the definition of certain kinds of languages more succinct.

But from what I understand xs:choice still only allows single element selection. Hence setting the MaxOccurs to unbounded like this should only mean that "any one" of the child elements can appear multiple times. Is this accurate?

No. The choice happens individually for every "repetition" of xs:choice that occurs due to maxOccurs="unbounded". Therefore, the code that you have posted is correct, and will actually do what you want as written.

If none of the above is working, you are probably working on EDI trasaction where you need to validate your result against an HIPPA schema or any other complex xsd for that matter. The requirement is that, say there 8 REF segments and any of them have to appear in any order and also not all are required, means to say you may have them in following order 1st REF, 3rd REF , 2nd REF, 9th REF. Under default situation EDI receive will fail, beacause default complex type is

<xs:sequence>
  <xs:element.../>
</xs:sequence>

The situation is even complex when you are calling your element by refrence and then that element in its original spot is quite complex itself. for example:

<xs:element>
<xs:complexType>
<xs:sequence>
<element name="REF1"  ref= "REF1_Mycustomelment" minOccurs="0" maxOccurs="1">
<element name="REF2"  ref= "REF2_Mycustomelment" minOccurs="0" maxOccurs="1">
<element name="REF3"  ref= "REF3_Mycustomelment" minOccurs="0" maxOccurs="1">
</xs:sequence>
</xs:complexType>
</xs:element>

Solution:

Here simply replacing "sequence" with "all" or using "choice" with min/max combinations won't work!

First thing replace "xs:sequence" with "<xs:all>" Now,You need to make some changes where you are Referring the element from, There go to:

<xs:annotation>
  <xs:appinfo>
    <b:recordinfo structure="delimited" field.........Biztalk/2003">

***Now in the above segment add trigger point in the end like this trigger_field="REF01_...complete name.." trigger_value = "38" Do the same for other REF segments where trigger value will be different like say "18", "XX" , "YY" etc..so that your record info now looks like:b:recordinfo structure="delimited" field.........Biztalk/2003" trigger_field="REF01_...complete name.." trigger_value="38">

This will make each element unique, reason being All REF segements (above example) have same structure like REF01, REF02, REF03. And during validation the structure validation is ok but it doesn't let the values repeat because it tries to look for remaining values in first REF itself. Adding triggers will make them all unique and they will pass in any order and situational cases (like use 5 out 9 and not all 9/9).

Hope it helps you, for I spent almost 20 hrs on this.

Good Luck