How to get XML Nodes of specified XML Data Type using XQuery

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C#

SQL-Server

I have an XML schema file and an XML document.Now I want the get the List of Nodes in the XML document by the specified data type in the XML schema file.
For example the XML Schema file is like

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <xsd:element name="Employee">
        <xsd:complextype>
            <xsd:sequence>
                <xsd:element name="FirstName" type="xsd:string" />
                <xsd:element name="MiddleName" type="xsd:string" />
                <xsd:element name="LastName" type="xsd:string" />
            </xsd:sequence>
        </xsd:complextype>
    </xsd:element>
</xsd:schema>

And the XML document is as follows

<employee>
    <firstname>Jacob</firstname>
    <middlename>V</middlename>
    <lastname>Sebastian</lastname>
</employee>

Now I want the get the Node by specifying the type of the XML node like

by specifying the XML node tye 'xsd:string' rather than by the node name First or MiddleName or LastName

I want to achieve this by using SQL server or C#

Thanks in advance