What is the DTD ?

DTD stands for Document Type Definition
Sharing a common DTD means businesses can share data
It is an optional document defining which tags make up a specific xml markup.
It also defines what sort of data the tags can contain
Adherence to a specific DTD makes the xml document VALID
Here is how a DTD is called by an XML file.

<!DOCTYPE winelist SYSTEM “myml.dtd”>

winelist is the root element of the xml file
myml.dtd is the name of the DTD document
What does a DTD document look like ?
The myml.dtd file contains the tag definitions

1 <!ELEMENT winelist (wine)*>
2 <!ELEMENT wine (name|price)*>
3 <!ELEMENT name (#PCDATA)*>
4 <!ELEMENT price (#PCDATA)*>

(note: the line numbers are not part of the dtd file, they have been added for explanation purposes only)
Line 1 defines the root xml element winelist as only containing the child element wine and no other
Line 2 defines wine to contain a name and price field only
Lines 3 and 4 define price and name as text only (#PCDATA)*

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