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ID, IDREF could someone please explain them :)

Posted on 2005-03-05
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Hi im trying to learn XML im very much a beginner :

Im trying to understand the concept and usage of IDREFs in XML. I belive there is also ID, IDREF and IDREFS. Im not sure if they can be used to uniquely identify something, but i would like to use this, if i could understand how it works ( i am also using a DTD ).

Would it please be possible for someone to explain what ID, IDREF and IDREFS is and if possible with examples explain why they would be used or how they could be used in XML.

Much appreciated.

Many thanks

GISVPN
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Question by:gisvpn
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by:dualsoul
ID: 13493678
ID - is used to provide some unique identifier for element.
IDREF - is used to reference some ID.  Generally it means that you can define IDREF with the same value as some existent ID.

This is just to ensure data integrity and consistency, to ensure you have a reference to existent element only.
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by:gisvpn
ID: 13499445
Hey Dualsoul thats great thanks for the post :)

Is there anyway in which you can give me a basic example ?
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dualsoul earned 2000 total points
ID: 13505128
yes, why not, in general let's consider following example:

<peoples>
  <man id="1" />
  <man id="3" />
</peoples>
<bids>
   <bid personId="1" /> <!-- Valid -->
   <bid personId="2" /> <!-- Invalid, there are on man with ID=2 -->
</bids>


, so if you declare man/@id as ID, and bid/@personId as IDREF to man/@id, you can control consistency, @personId can have only value from existent @id. It's like a foreign key in RDBMS.
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