Describe Process for creating a DTD

<?xml version="1.0"?> 
<CATALOG>
 <BOOK>
 <TITLE>A Certain Justice</TITLE>
<AUTHOR>P.D. James</AUTHOR>
 <YEAR-PUBLISHED>1998</YEAR-PUBLISHED>
 <ISBN>0375401091</ISBN>
 </BOOK> 
<BOOK>
<TITLE>Ashworth Hall</TITLE>
<AUTHOR>Anne Perry</AUTHOR>
 < YEAR-PUBLISHED>1997</YEAR-PUBLISHED>
<ISBN>0449908445</ISBN>
</BOOK>
<BOOK>
<TITLE>L.A. Confidential< /TITLE>
<AUTHOR>James Ellroy</AUTHOR>
 < YEAR-PUBLISHED>1997</YEAR-PUBLISHED>
<ISBN>0446674249</ISBN>
</BOOK>
<BOOK>
<TITLE>Shadow Woman</TITLE>
<AUTHOR>Thomas Perry</AUTHOR>
 <YEAR-PUBLISHED>1997</YEAR-PUBLISHED>
<ISBN>0679453024</ISBN>
</BOOK>
</CATALOG>

Determine the Root Element

1. Determine the root element of the document. The root element in this example is CATALOG.
2. List all the other elements used in the document.

1. BOOK,
2. TITLE,
3. AUTHOR,
4. YEAR-PUBLISHED, and
5. ISBN.

Create Document Tree structure

After listing all the elements, create a document tree structure for them. This figure represents the document tree for the elements in the book catalog:

Note whether elements need to appear in a specific order. In the book catalog example, assume the elements

1. TITLE,
2. AUTHOR,
3. YEAR-PUBLISHED, and
4. ISBN

must appear in that order. Also note whether certain elements have content that must be present, can be present, or may be present multiple times. In this example, it is clear that you need one and only one TITLE and one and only one YEAR-PUBLISHED element for each BOOK element. For now, you will use only one AUTHOR element for each BOOK element as well, although that could change. Any number of BOOK elements can exist, though there should be at least one book present to consider this a catalog.
Finally, you will note which elements will contain text and which will only contain other elements. The elements that will only contain other elements in this example are the root element CATALOG and the BOOK element. All other elements will contain character data.

Creating the DTD

  <!DOCTYPE CATALOG [ 
 <!ELEMENT CATALOG (BOOK)+>
  <!ELEMENT BOOK (TITLE,AUTHOR,YEAR-PUBLISHED,ISBN?)> 
  <!ELEMENT TITLE (#PCDATA)> 
  <!ELEMENT AUTHOR (#PCDATA)> 
  <!ELEMENT YEAR-PUBLISHED (#PCDATA)>
  <!ELEMENT ISBN (#PCDATA)> 
]> 

This DTD indicates the following:

1. The root element is CATALOG.
2. The CATALOG element contains one or more BOOK elements. This is indicated by the + suffix.
3. The BOOK element contains TITLE, AUTHOR, YEAR-PUBLISHED, and ISBN, in this order. Each of these can contain only character data.
4. ISBN need not be present, but if it is present, no more than one ISBN element can be used per BOOK element, and it will be the last element in the BOOK element set.

DTD syntax characters