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Varieties of Selection (cont)

We can view a relation as defining a tuple space
  • assume relation R with attributes a1,...,an
  • attribute domains of R specify a n-dimensional space
  • each tuple (v1,v2,...,vn) ∈ R is a point in that space
  • queries specify values/ranges on N≥1 dimensions
  • a query defines a point/line/plane/region of the n-d space
  • results are tuples lying at/on/in that point/line/plane/region
E.g. if N=n, we are checking existence of a tuple (at a point)