How to create an XML language that is the intersection of two XMLlanguag

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

Suppose person #1 creates an XML language for Books:

    <xs:element name="Books">
        ...
    </xs:element>

Person #2 creates an XML language for Magazines: 
    
    <xs:element name="Magazines">
        ...
    </xs:element>

Now, person #3 can reuse them to create an XML language that is the union of Books and Magazines: 
    
    <xs:element name="BookStore">
        <xs:complexType>
            <xs:choice>
                <xs:element ref="Books" />
                <xs:element ref="Magazines" />
            </xs:choice>
        </xs:complexType>
    </xs:element>

Neat! We can create an XML language that is the union of two XML languages, without any changes to them.

What about intersection, can we create an XML language that is the intersection of two XML languages?

Suppose person #4 creates an XML language consisting of a mixture of an arbitrary number of <A> and <B> elements: 
    
    <xs:group name="As-and-Bs">
        <xs:sequence maxOccurs="unbounded">
            <xs:element name="A" minOccurs="0"> ... </xs:element>
            <xs:element name="B" minOccurs="0"> ... </xs:element>
        </xs:sequence>
    </xs:group>

Person #5 creates an XML language consisting of a mixture of an arbitrary number of <B> and <C> elements: 
    
    <xs:group name="Bs-and-Cs">
        <xs:sequence maxOccurs="unbounded">
            <xs:element name="B" minOccurs="0"> ... </xs:element>
            <xs:element name="C" minOccurs="0"> ... </xs:element>
        </xs:sequence>
    </xs:group>

Now, person #6 wants to reuse them to create an XML language that is the intersection of the two languages. 

How would person #6 create this intersection language (without any change to the As-and-Bs language or the Bs-and-Cs language)?

/Roger