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<html>
<head>
<title>ACID RDBMS</title>

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<font size="+1">

<h2>ACID RDBMS</h2>

<hr>

   <blockquote>
     <b>Atomicity:</b> In a sequence of steps either all actions occur or
     none.<br /><br />

     <blockquote>
     <b>Example:</b> Moving money from savings to checking accounts.
     </blockquote>
     
     <b>Consistency:</b> The database is transformed from one valid
     state to another valid state.<br /><br />

     <blockquote>
     <b>Example:</b> If someone moves 10,000$ from their checking
     account that information is logged.  If it can't be logged then
     the money is not transferred.
     </blockquote>

     <b>Isolation:</b>  
     The results of a transaction are invisible to other
     transactions until the transaction is complete. 

     <br /><br />

     <blockquote>
     <b>Example:</b> If someone an accountant starts a report at 1700
     and Joe User deposits 100$ into their account at 1701.  The
     report, even if it finishes at 1702 will not show the changes
     made by Joe User.
     </blockquote>

     <b>Durability:</b> Once committed (completed), the results of a
     transaction are permanent and survive future system and media
     failures.

     <blockquote>
     <b>Example:</b>  Once your seat is reserved on an airplane, even
     if the system crashes the moment it finishes writing that information
     in the database your seat will still be reserved.
     </blockquote>
   </blockquote>

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<hr />
<address><a href="mailto:tristancohen@yahoo.com">tristancohen@yahoo.com</a></address>

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by admin — last modified 2003-04-28 10:46
 

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