Explain: DTD's in XML
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Please discuss the following question: Describe how you would create and declare DTD's in XML.
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Solution Summary
In a five page word document, this solution provides ideas to create and declare DTD's in XML.
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** Please see the attached file for the solution **
DTDs can be declared inline in your XML code or they can reference an external file.
This is an example of an internal DTD.
<?xml version="1.0"?>
<!DOCTYPE message [
<!ELEMENT message (to,from,subject,text)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT subject (#PCDATA)>
<!ELEMENT text (#PCDATA)>
]>
<message>
<to>Dave</to>
<from>Susan</from>
<subject>Reminder</subject>
<text>Don't forget to buy milk on the way home.</text>
</message>
Line 2 defines the <message> element as having the four child elements: <to>, <from>, <subject> and <text>.
<!ELEMENT message (to,from,subject,text)>
This line defines the <to> element to be of type PCDATA.
<!ELEMENT to (#PCDATA)>
Here is the same document with an external DTD reference:
<?xml version="1.0"?>
<!DOCTYPE message SYSTEM "message.dtd">
<message>
<to>Dave</to>
<from>Susan</from>
<subject>Reminder</subject>
<text>Don't forget to buy milk on the way home.</text>
</message>
And here is the referenced DTD file. You can open it in Explorer and select View | Source as above.
<?xml version="1.0"?>
<!ELEMENT message (to,from,subject,text)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT subject (#PCDATA)>
<!ELEMENT text (#PCDATA)>
In DTD, elements are declared using an element declaration with the following syntax:
<!ELEMENT element-name (element-content)>
Empty elements
Empty elements use the empty keyword. Move the mouse over the text for additional information.
<!ELEMENT ...
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