Create a DTD which describes the structure of the document which you prepared in Question 1. Make sure that you use all appropriate DTD ingredients to constrain valid documents as much as possible.
Make sure that your DTD has the following two features:
(a) Use IDREFs in your DTD to include more data about users and refer to those users elsewhere in doc; and
(b) Your DTD should contain one or more parameter entities.
You should modify your XML document from Question 1 such that it now contains a reference to the DTD schema. Include in your submission a screenshot that proves that your instance document is valid over the DTD. For example, if you use xmllint in Linux, take a screenshot of the start of the output. As an aother example, if you use an editor such as Blue?sh, take a screenshot after you have run the DTD validation.