Validating XSD and reusing elements - xsd

Question

I have an XSD that is used for multiple services.
In the XSD, I have and "Order" complex type.
Another system calls my service, and sends "Order" info, and my service does some stuff with the "Order" info that is sent to my service.
In "Order", I have a few elements, for example: "foo" and "bar".
My goal is to use this XSD for multiple services, for instance, serviceA and serviceB.
Both services use "Order", but for serviceA I want to make "foo" required, but for serviceB I do not want "foo" required.
Can I control this in the XSD, or is the only way to make "foo" optional, and check in code (after the service call) that it is not empty if the service call is from serviceA?

Answer 1

You can obtain that with derivation. Suppose you have a type Order containing optional foo and bar:
<xs:complexType name="Order">
<xs:sequence>
<xs:element ref="foo" minOccurs="0"/>
<xs:element ref="bar" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
I'm assuming you have a root element that supports the different services:
<xs:element name="services">
<xs:complexType>
<xs:choice>
<xs:element name="serviceA" type="ServiceAType" />
<xs:element name="serviceB" type="ServiceBType" />
</xs:choice>
</xs:complexType>
</xs:element>
If serviceB allows optional foo and bar, you can simply declare the type of serviceB as Order, or create a ServiceBType which extends Order:
<xs:complexType name="ServiceBType">
<xs:complexContent>
<xs:extension base="Order"/>
</xs:complexContent>
</xs:complexType>
If you want ServiceAType to restrict the contents of Order so that foo is required, then you can implement it as a restriction of Order:
<xs:complexType name="ServiceAType">
<xs:complexContent>
<xs:restriction base="Order">
<xs:sequence>
<xs:element ref="foo" minOccurs="1"/>
<xs:element ref="bar" minOccurs="0"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
Now you can have <serviceB> containing no elements, containing <foo>, <bar> or <foo> followed by <bar>. <serviceA> will allow <foo> followed by <bar> or <foo> but nothing else.