An Extra Problem: the beer database

1
An Extra Problem the beer database

• likes(drinker, beer)
• visits(drinker, bar)
• serves(bar, beer)
• Obs. 1 We assume that every drinker likes at
  least one beer, every drinker goes to at least
  one bar and every bar serves at least one beer.

2
1. all drinkers who go to a bar that serves
beer(s) they like

• Obs.1 the bar can also serve beers they dont
  like
• Obs.2 drinkers can also go to other bars, where
  they dont like the beer
• I) relational algebra
• ?drinker(likes visits serves) (? A)
• II) tuple relational calculus
• t ? l ?likes ( tdrinker ldrinker ?
  ? v ?visits ( tdrinker
  vdrinker ? ? s ?serves (vbar
  sbar ? lbeer sbeer ) ) )
• III) domain relational calculus
• ltdgt ?be,ba (ltd,begt ?likes ? ltd,bagt ?visits ?
  ltba,begt ?serves )

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2. all drinkers who go to bars that serve a
beer they dont like

• Obs.1 drinkers can also go to other bars, where
  they like the beer
• I) relational algebra
• ?drinker(?drinker,beer (visits serves) -
  likes) (? B)
• II) tuple relational calculus
• t ?v ?visits ( tdrinker vdrinker ?
  ?s ?serves (vbar sbar ? ? l
  ?likes ( tdrinker ldrinker gt lbeer ?
  sbeer ) ) )
• III) domain relational calculus
• ltdgt ?be,ba (ltd,bagt ?visits ? ltba,begt ? serves
  ? ? b (ltd,bgt ?likes gt b
  ? be) )

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3. all drinkers who only go to bars that serve a
beer they like

• Obs.1 the bar has to serve at least a beer they
  like, but can serve others
• Obs.2 drinkers dont have to go to all bars that
  serve the beers they like
• I) relational algebra
• ?drinker (visits ) - ?drinker (visits -
  ?drinker,bar (serves likes ))
• II) tuple relational calculus
• t ? v ?visits ( tdrinker vdrinker gt
  ? l ?likes ( tdrinker ldrinker
  ? ? s ?serves ( lbeer sbeer ?
  sbar vbar ) ) )
• III) domain relational calculus
• ltdgt ?ba (ltd,bagt ?visits gt ? be (ltba,begt
  ?serves ? ltd,begt ? likes) )

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4. all drinkers who only go to bars that serve NO
beer they like

• I) relational algebra
• ?drinker (visits ) - A
• II) tuple relational calculus
• t ? v ?visits ( tdrinker vdrinker ?
  ? s ?serves (sbar vbar ) gt
  ? ? l ?likes ( tdrinker ldrinker ?
  lbeer sbeer ) )
• III) domain relational calculus
• ltdgt ?ba,be (ltd,bagt ?visits ? ltba,begt ? serves
  gt ltd,begt ? likes)

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5. all drinkers who only go to bars that serve
only beer they like

• I) relational algebra
• ?drinker (visits ) - B
• II) tuple relational calculus
• t ? v ?visits ( tdrinker vdrinker ?
  ? s ?serves (sbar vbar ) gt
  ? l ?likes ( tdrinker ldrinker ?
  lbeer sbeer ) )
• III) domain relational calculus
• ltdgt ?ba, be (ltd,bagt ?visits ? ltba,begt ?serves
  gtltd,begt ? likes)

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6. all the drinkers who like all the beers that
are served somewhere

• Obs. 1 the drinkers may also like some beers
  that are not served anywhere.
• I) relational algebra
• likes ?beer(serves )
• II) tuple relational calculus
• t ? v ?visits ( tdrinker vdrinker ?
• ? s ?serves (? l ?likes ( tdrinker
  ldrinker ? lbeer sbeer ) )
• III) domain relational calculus
• ltdgt ? b (ltd,bgt?visits ?
  ?ba, be
  (ltba,begt ?serves gt ltd,begt ? likes)