XSD two elements with the same inner structure - xsd

Question

I am working with an xsd, trying to get it to validate an xml.
The xml is used to create objects. There are two types of objects that can be created by the elements in the list: SC and SMSC. SMSC is an SC, and extends it.
SMSC doesn't contain any new properties. From the perspective of the xml, an SMSC is identical to an SC in every way, except that the elements that define its properties are wrapped by <SMSC> tags instead of <SC> tags.
Our XSD looks like this:
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name='Definitions'>
<xsd:complexType>
<xsd:sequence>
<xsd:element maxOccurs="unbounded" name="SC">
<!--SNIP properties of SC and SMSC -->
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
Is there a way to change this to allow either SC or SMSC as the element, other than duplicating all of the property definitions in an SMSC element? We don't want to have to double the length of the document and duplicate all of the property definitions.
As it stands, the only validation error we have in our XML is where we have an SMSC element. If there isn't a way to fix this without duplicating all the property definitions we'll leave it as-is, but we'd obviously prefer to eliminate the warning this throws if practical.

Answer 1

While it is confusing by tags instead of tags, I would think that below is either answering your question, or elicits better explanations.
So, what you see is avoiding duplication; you don't actually need the additional type SMSC (see Definitions2), but I've put it just in case (Definitions). Making the SMSC element of the SC type would work exactly the same.
The difference between Definitions / Definitions2 and Definitions3 is that one uses substitution groups instead of choices. I personally prefer substitution groups to choices, yet is not that uncommon to run into issues related to substution groups (i.e. they are poorly supported here and there).
<?xml version="1.0" encoding="utf-8" ?>
<!-- XML Schema generated by QTAssistant/XSD Module (http://www.paschidev.com) -->
<xsd:schema targetNamespace="http://tempuri.org/XMLSchema.xsd" xmlns="http://tempuri.org/XMLSchema.xsd" elementFormDefault="qualified" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:complexType name="SC">
<xsd:sequence>
<!-- Stuff goes here -->
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="SMSC">
<xsd:complexContent>
<xsd:extension base="SC"/>
</xsd:complexContent>
</xsd:complexType>
<xsd:element name="Definitions">
<xsd:complexType>
<xsd:choice maxOccurs="unbounded">
<xsd:element name="SC" type="SC"/>
<xsd:element name="SMSC" type="SMSC"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>
<!-- Another way -->
<xsd:element name="Definitions2">
<xsd:complexType>
<xsd:choice maxOccurs="unbounded">
<xsd:element name="SC" type="SC"/>
<xsd:element name="SMSC" type="SC"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>
<xsd:element name="Definitions3">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="SC" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="SC" type="SC" />
<xsd:element name="SMSC" type="SMSC" substitutionGroup="SC" />
</xsd:schema>