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Extract, Transform and Load or ETL for short, is a process of data manipulation where information from one source is Extracted, that information is then Transformed, which may include such operatins as data cleansing or validation, essentially so the data fits in with business needs. The resulting dataset is then Loaded into another storage system. An example of a practical applications of this is integrating legacy systems into a business.

A small example of this process can be seen here where a very basic ETL PHP script attaches to a message queue. Software available for ETL includes Pentaho Data Integration, an open source app. Another one I have come across which doesn't market itself as a pure ETL program and if comparing it with the ETL process is rather limited, is DBMaker. An example of parsing Google search result pages can be found here allthough use of the script for anything other than curiosity is probably unadvisable!

The snippet below will nicely extract a portion of a string between two delimeters. 

  function returnSubstrings($text, $openingMarker, $closingMarker) {
   $openingMarkerLength = strlen($openingMarker);
   $closingMarkerLength = strlen($closingMarker);
 
   $result = array();
   $position = 0;
   while (($position = strpos($text, $openingMarker, $position)) !== false) {
     $position += $openingMarkerLength;
     if (($closingMarkerPosition = strpos($text, $closingMarker, $position)) !== false) {
       $result[] = substr($text, $position, $closingMarkerPosition - $position);
       $position = $closingMarkerPosition + $closingMarkerLength;
     }
   }
   return $result;
  }