finding gems by all of the same authors?

[Rich Morin]

I'm trying to work up some example queries for a project
related to RubyGems (archives of Open Source Ruby code).
I'm not at all sure how to code a query such as:

  What Gems were written by all of the same authors?

That is, if this Gem was written by Alice and Bob, I want
to find others that were also written only by these two.


Here is some total science fiction I wrote:

  SELECT DISTINCT ?gem
  ORDER BY        ?gem
  WHERE {
    { SELECT DISTINCT ?author AS ?set_1
      WHERE { item:foo-1.2.3-x86  spec:author  ?author . } }

    { SELECT DISTINCT ?author AS ?set_2
      WHERE { ?gem                spec:author  ?author . } }
  }
  FILTER(?set_1 = ?set_2)


Is this approximately on the right track?  Any suggestions
or other clues?

-r


P.S.  It would also be nice to answer a related question:

  What Gems were written by at least the same authors?

That is, if this Gem was written by Alice and Bob, I want
to find others that were also written by them (and possibly
others).

-- 
http://www.cfcl.com/rdm            Rich Morin
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