To make it easier to read and to maintain (I presume this is going to be some sort of template), it may be easiest to represent the data in YAML (YAML::Syck for speed). For some elements, you may need hashes, for others array - writing it down in YAML notation makes it easy to adjust your data structure to suit the need.

For instance, you could represent your example as follows:

slides:
 -
   no:    1
   type:  ppBLAHBLAH
   title: My title
   elements:
    - 
      type:    picture
      path:    /my/path
      width:   100
      height:  50
    - 
      type:    text box
      text: |
               A bunch of flowing
               text
      style:   italics
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