xsd - Define an XML element that must be empty and has no attributes

Question

I needed to define an XML element that has no sub-elements or any content at all, and has no attributes.

This is what I am doing:

<xs:element name="myEmptyElement" type="_Empty"/>
<xs:complexType name="_Empty">
</xs:complexType>

This appears to work fine, but I have to wonder if there is a way to do this without having to declare a complex type. Also, if there is anything wrong with what I have, please let me know.

Anticipating that someone might be curious why I would need such an element: It is for a SOAP operation that does not require any parameter values.

Answer 1

(1) You could avoid defining a named xs:complexType:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="myEmptyElement">
    <xs:complexType/>
  </xs:element>
</xs:schema>

(2) You could use a xs:simpleType instead of a xs:complexType:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="myEmptyElement">
    <xs:simpleType>
      <xs:restriction base="xs:string">
        <xs:maxLength value="0"/>
      </xs:restriction>
    </xs:simpleType>
  </xs:element>
</xs:schema>

(3) You could use fixed="" ^{_{[credit: @Nemo]}}:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="myEmptyElement" type="xs:string" fixed=""/>
</xs:schema>

(4) But note that if you avoid saying anything about the content model:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="myEmptyElement"/>
</xs:schema>

You'll be allowing any attributes on and any content in myEmptyElement.