I have a shared XML schema which has not namespace declared department.xsd

<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
            elementFormDefault="qualified"
            attributeFormDefault="unqualified"
            version="1-0">
    
    <xs:complexType name="Department">
        <xs:sequence>
            <xs:element name="Name"/>
            <xs:element name="Manager"/>
        </xs:sequence>
    </xs:complexType>
</xs:schema>

And I want to import Department.xsd in Company.xsd which has the namespace MainNameSpace

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns="MainNameSpace"
           xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:m="MainNameSpace" <!--New NameSpace-->
           targetNamespace="MainNameSpace"
           elementFormDefault="unqualified"
           attributeFormDefault="unqualified">

    <xs:import schemaLocation="Department.xsd" namespace="MainNameSpace"/> <!--Not working-->

    <!--<xs:import schemaLocation="Department.xsd"/> Not working-->
    <!--<xs:include schemaLocation="Department.xsd"/> Not working-->


    <xs:element name="company" type="Company"/>

    <xs:complexType name="Company">
        <xs:sequence>
            <xs:element name="Name" type="xs:string"/>
            <xs:element name="Department" type="m:Department"/>
        </xs:sequence>
    </xs:complexType>

</xs:schema>

However when I compile the schema in C#, I got error “‘Type ‘MainNameSpace:Department’ is not declared.'”. From what I read, include another schema without namespace will use the root namespace for the imported schema, but why MainNameSpace:Department cannot be found?

    var schema = new XmlSchemaSet();

    schema.Add(null, Path.Combine(baseDirectory, "Department.xsd"));
    schema.Add(null, Path.Combine(baseDirectory, "Company.xsd"));

    schema.Compile();