DTD and Definition

We see big use of XML (eXtensible markup language) everywhere, especially in web programming and web services we do have to use XMLs. How is a simple XML file?

<?xml version="1.0"?>

The below example we are using the given XML data we have the tags like <user> </user> but how do we define those? Here we have the answer DTD(Document Type Definition). Simply we define a DTD file like this:

<!DOCTYPE user
<!ELEMENT user(name,lastname,country)>
<!ELEMENT lastname (#PCDATA)>
<!ELEMENT country (#PCDATA)>

here we have defined a definition for our xml schema. If I explain these attributes:

  • !DOCTYPE means that user is the root element of the defition and xml schema,
  • !ELEMENT user (name,lastname,country) defines that our schema will have three elements,
  • !ELEMENT defines each element
  • #PCDATA is last of all defines parse able text data

In xml the raw data has to be valid which does indicate that it needs to be a well formatted xml document which also identifies the rules of DTD. With the DTD you can identify your own XML tag format and add as many attributes as you wish.

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