You define the syntax and structure of elements using a document type definition (DTD), and you declare that definition in a document using a document type declaration. We've seen that you use the <!DOCTYPE> element to create a document type declaration. This element can take many different forms, as you see here (here, URL is the URL of a DTD, and rootname is the name of the root element); we'll see all these forms in this chapter:
To use a DTD, you need a document type declaration, which means that you need a <!DOCTYPE> element. The <!DOCTYPE> element is part of a document's prolog. Here's how I add a document type declaration to the document ch02_01.xml that we developed in the previous chapter: <?xml version = "1.0" standalone="yes"?> <!DOCTYPE DOCUMENT [ . . . ]> <DOCUMENT> <CUSTOMER> <NAME> <LAST_NAME>Smith</LAST_NAME> <FIRST_NAME>Sam</FIRST_NAME> </NAME> <DATE>October 15, 2003</DATE> <ORDERS> <ITEM> <PRODUCT>Tomatoes</PRODUCT> <NUMBER>8</NUMBER> <PRICE>.25</PRICE> </ITEM> . . . <ITEM> <PRODUCT>Asparagus</PRODUCT> <NUMBER>12</NUMBER> <PRICE>.95</PRICE> </ITEM> <ITEM> <PRODUCT>Lettuce</PRODUCT> <NUMBER>6</NUMBER> <PRICE>.50</PRICE> </ITEM> </ORDERS> </CUSTOMER> </DOCUMENT> Now it's up to us to supply the actual DTD that is part of this <!DOCTYPE> element. |