question4.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE library [
    <!ELEMENT library (book+)>
    <!ELEMENT book (title, author+, pageNo, price)>
    <!ATTLIST book ISBN CDATA #REQUIRED>

    <!ELEMENT title (#PCDATA)>
    
    <!ELEMENT author (firstName, middleName?, lastName, phone, email)>
    <!ATTLIST author title (mr|ms|mrs) "ms">
    <!ELEMENT firstName (#PCDATA)>
    <!ELEMENT middleName (#PCDATA)>
    <!ELEMENT lastName (#PCDATA)>
    <!ELEMENT phone (#PCDATA)>
    <!ELEMENT email (#PCDATA)>
    
    <!ELEMENT pageNo (#PCDATA)>
    
    <!ELEMENT price (#PCDATA)>
    <!ATTLIST price currency (NPR|INR|USD) #REQUIRED>
]>
<library>
    <book ISBN="1234567890">
        <title>XML Guide</title>
        <author title="mr">
            <firstName>John</firstName>
            <middleName>A.</middleName>
            <lastName>Doe</lastName>
            <phone>123456789</phone>
            <email>john.doe@example.com</email>
        </author>
        <author title="ms">
            <firstName>Jane</firstName>
            <lastName>Smith</lastName>
            <phone>987654321</phone>
            <email>jane.smith@example.com</email>
        </author>
        <pageNo>250</pageNo>
        <price currency="USD">599</price>
    </book>
</library>