Relations and Cell Arrays

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• Misc
  • No office hours for Nick this week
• Questions?
• Relations
  • So far: relation = set of ordered pairs of numbers
  • Non-numeric relations
    • e.g., colors of things
    • { ... {Nick’s Jacket, red }, {Baldwin’s shoes, brown}, ... }
  • n-ary relations
    • Ordered tuples
    • Sum-of: x = y + z
      • { ... (4,3,1), (7.5,10.9,-3.4), ... }
  • Non-numeric n-ary relations
    • { ... (student-name, gpa, id-number, ... ), ... }
  • Lists as attributes
    • For instance, “customers also liked...” list in online store
      • { ... (watch, $88.95, jacket, camera), ... (jacket, $129.99, watch)
    • Can’t have tuples with different numbers of members in the same relation
    • So use two relations, with multiple tuples in the 2nd to represent the list
      • Products: { ... (watch, $88.95), (jacket,$129.99), ... }
      • Also-liked: { ... (watch,jacket), (watch,camera), ...}
  • Terminology
    • “Record” = tuple in relation
    • “Attribute” = member of tuple
      • As in “the name attribute”
  • Start working on lab problems
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