DTD Components

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Document Type Declaration

An XML document begins by identifying itself as an XML document. The following represents a typical introduction to an XML document:

<?xml version="1.0" standalone="yes" encoding="UTF-8"?> <!DOCTYPE Order [ . . . <! -- DTD specifications --> ]

The first expression declares the XML version to which the document conforms. Our document is a version 1.0 document.

Our document is also a standalone XML document, without references to other documents. Since it is a standalone document, it must contain its DTD, if one exists. It is possible for a simple standalone XML document to have no DTD.

Finally, the first line states that the document can contain only 8-bit ASCII characters. An XML document can contain 16-bit characters, similar to Unicode in Java. If this document were a 16-bit document, the required syntax would be encoding= 'UTF-16.'

The next line in the type declaration identifies the document type as Order. An Order comprises all the elements and attributes specified. These directives will be included inside the braces ([]).

The exclamation point is a tag that represents a comment. The text between <! and the closing > will be ignored by an XML parsing program.

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