Given an XML layout like this, I’m trying to create a XSD schema to validate it.
<RootNode>
<ChildA />
<ChildC />
<ChildB />
<ChildB />
<ChildA />
</RootNode>
The requirements are as follows:
- ChildA, ChildB and ChildC may occur in any order. (
<xs:sequence>unsuitable) - ChildA is mandatory but may occur multiple times.
- ChildB is optional and may occur multiple times.
- ChildC is optional and may occur once only.
The technique I usually use to create an unordered list of nodes is to use a <xs:choice maxOccurs="unbounded"> with each possible node in the list, however, I am unable to create the minOccurs="1" constraint on ChildA and the maxOccurs="1" contraint on ChildC. (The # of occurances of the choice takes precedence over those of the elements here).
<xs:element name="RootNode">
<xs:complexType>
<xs:choice minOccurs="1" maxOccurs="unbounded">
<xs:element name="ChildA" minOccurs="1"/>
<xs:element name="ChildB" />
<xs:element name="ChildC" maxOccurs="1"/>
</xs:choice>
</xs:complexType>
</xs:element>
Update: In XSD 1.1m some of the constraints on
all-groups have been lifted. See the answers here and here.Not a simple one but seems doable. Difficult part here is that Schema definitions must be deterministic. Approach I used was to visualize the problem by drawing a finite state automata of it and then to write a regular expression that corresponded that automata. It is not at all as complicated as it might sound. Still, using some other validation system would have likely provided simpler answer.
I have done some testing but missing out some special cases is easy. Please comment if you spot an error.
…and here is the code: