XSD Validation with If Else Possibility - xsd-validation

Question

Just trying to figure out if below scenario can be achieved through XSD schema level validation.
E.g-
<PreferredPlan>
This tag can have Values - Family or Single
if I got the value as "Family", I should be having below xml elements.
<Family>
<tag1></tag1>
<tag2></tag2>
If "Single" value is captured, I should have below tags.
<Single>
<tag3></tag3>
<tag4></tag4>
</Single>

Answer 1

One simple way to define this would look something like this:
<xs:element name="PreferredPlan">
<xs:complexType>
<xs:choice>
<xs:element ref="Family"/>
<xs:element ref="Single"/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name="Family">
<xs:complexType>
<xs:sequence>
<xs:element ref="tag1"/>
<xs:element ref="tag2"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="Single">
<xs:complexType>
<xs:sequence>
<xs:element ref="tag3"/>
<xs:element ref="tag4"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="tag1" type="xs:string"/>
<xs:element name="tag2" type="xs:string"/>
<xs:element name="tag3" type="xs:string"/>
<xs:element name="tag4" type="xs:string"/>
This allows
<PreferredPlan>
<Family>
<tag1/>
<tag2/>
</Family>
</PreferredPlan>
and
<PreferredPlan>
<Single>
<tag3/>
<tag4/>
</Single>
</PreferredPlan>
and forbids
<PreferredPlan>
<Family>
<tag3/>
<tag4/>
</Family>
</PreferredPlan>