First of all, I read all the materials we had at hand and tried to understand them, especially the concepts and fonctions of DTD, DOM and XML, etc. Then I created the above simple DTD file and XML file. I looked at the examples which call the XML in a JSP page. As usual I picked up some examples and did the copy and paste work. And then I did some necessary changes there.
XML works very well with JSP. But it seems that we cannot do anythig in real interaction with it. Perhaps it can, but I haven't found it yet. Compared with SQL, I think SQL is easier to malipulate data. Once the table is created, it is easier to insert or delete data from it. E.g. here with the address book, it will be better if we can add a new contact into it and delete a contact that we do not want to keep any more, instead of just showing the content of it.