Question

<xs:element name="qualificationRequired" type="ExtendedQualification"/>
    <xs:complexType name="ExtendedQualification">
        <xs:complexContent>
            <xs:extension base="qualifications">
                <xs:element name="other">
                    <xs:element name="skills" type="xs:string"/>
                    <xs:element name="languages" type="xs:string"/>
                </xs:element>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType> 
    </xs:sequence>
</xs:complexType> //closes another complexType above

My validator returns the following errors:

Validator Error: s4s-elt-must-match.1: The content of ‘sequence’ must
match (annotation?, (element | group | choice | sequence | any)*). A
problem was found starting at: complexType. LINE 2

Validator Error 2: src-resolve: Cannot resolve the name
‘ExtendedQualification’ to a(n) ‘type definition’ component. LINE 1

why is this happening?

Answer 1

<xs:sequence> can not contain an <xs:complexType> as a child. You have to put it elsewhere. Either wrap it in an element, effectively making it a nested type, or put it directly in the <xs:schema> element as a global type.

Just as the error message says, the only tags you can put inside an <xs:sequence> are:

• <xs:element>
• <xs:group>
• <xs:choice>
• <xs:sequence>
• <xs:any>

Also, <xs:extension> cannot have <xs:element> tags as children. You have to wrap them in an <xs:sequence>, <xs:choice>, <xs:all>, etc. depending on what you want to achieve.

Finally, <xs:element> can’t contain other <xs:element> tags as children. You have to wrap them in a sequence/choice/all, etc. and then in <xs:complexType> to define a nested type. Or move it all outside to serve as a global type.

Here’s a valid document defining what you’re trying to do above. I don’t have insight into the whole document though, so it might need adjustments depending on the context.

<xs:schema version="1.0"
       xmlns:xs="http://www.w3.org/2001/XMLSchema"
       elementFormDefault="qualified">
<xs:complexType name="blah">    <!-- You said there was a complexType open, I added its opening tag and gave it a placeholder name -->           
    <xs:sequence>               
        <xs:element name="qualificationRequired" type="ExtendedQualification"/>            
    </xs:sequence>
</xs:complexType>
<xs:complexType name="ExtendedQualification"> <!-- the complexType is now removed from your sequence and is a global type-->
    <xs:complexContent>
        <xs:extension base="qualifications">
            <xs:sequence> <!-- you can't have an element here, you must wrap it in a sequence, choice, all, etc. I chose sequence as it seems to be what you meant -->
                <xs:element name="other">
                    <xs:complexType> <!-- same here, an element can't contain other element tags as children. For a complex element, you need a complexType. I defined it as a nested type -->
                        <xs:sequence> <!-- even complexType can't have element tags as children, again, I used a sequenct -->
                            <xs:element name="skills" type="xs:string"/>
                            <xs:element name="languages" type="xs:string"/>
                        </xs:sequence>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:extension>
    </xs:complexContent>
</xs:complexType> 
</xs:schema>