Ahhh fairynuff, I should have provided more information about the interfaces... okay, there you go:

• get_xml_files
  1. input: a (exist) directory
  2. objective: glob all xml files in the directory
  3. output: a list of filename.xml or empty list
• extract_file
  1. input: a list of xml files
  2. objective:
     1. parse the xml file (using XML::Simple)
     2. find a specific tag, e.g. IMPRESSIONS
  3. output: write to STDOUT the filename.xml and the IMPRESSIONS found

I think that should answer your question about the interface? I know that functionality can be done in one line by

    grep IMPRESSIONS *.xml

But again it's only an example...

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