I'll get into why and how.

Some spectrums:

  1. number of items aggregated
  2. degree of information compression (compressing info into a single word is the ultimate compression; a phrase, sentence, title, or headline is high compression, a summary is a bit less compression)
  3. which levels of information compression are available (does it just have a full text and a title, or does it also have a table of contents with sections and sub sections, with summaries for each section?)

See also

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