Creating/updating an xml file from a mysql database table with php

I have a javascript image gallery which is getting data from an XML file. Im in the process of building a backend function in order for someone else to easy update the gallery. All the data required in the XML file, is available to me from a table in my database.

<?xml version="1.0" encoding="UTF-8"?>
 <portfolio>
 <items> 
     <item>
         <thumbnail>images/banner001.jpg</thumbnail>
         <preview>images/preview.jpg</preview>
         <category>banner</category>
         <description>Swatch MTV </description>
     </item>
     <item>
         <thumbnail>images/banner002.jpg</thumbnail>
         <preview>images/preview.jpg</preview>
         <category>banner,campaign</category>
         <description>Nike iD</description>
     </item>
     <item>
         <thumbnail>images/banner003.jpg</thumbnail>
         <preview>images/preview.jpg</preview>
         <category>banner</category>
         <description>Sony Handycam</description>
     </item>
     <item>
         <thumbnail>images/banner006.jpg</thumbnail>
         <preview>images/preview.jpg</preview>
         <category>banner</category>
         <description>Statoil App kampagne</description>
     </item>     
     <item>
         <thumbnail>images/design006.jpg</thumbnail>
         <preview>images/preview.jpg</preview>
         <category>web</category>
         <description>Hempel Website design</description>
     </item>
 
 </items>
 </portfolio>
 

In this regard I have a couple of questions (please keep in mind that im fairly new to php):

1. which is the better/easier option: update the existing xml file or simply overwrite the entire xml file with newer/updated data?


2. how do I create the same xml format using php?


3. I have been looking at both SimpleXML and the DOMDocument. Which one is better/easier to use in my case?

I would be grateful for any help you guys can give me. If posting code, please include a short description/explanation.

Please let me know if you need anything clarified.

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