Nesting and Unnesting

• … then ? (B, copies) =

title

author

publ

pages

date

Moby Dick

Melville

Moby Dick

Melville

Marmion

Scott

Prentice Hall

McGraw Hill

613

1971

542

1942

null

null

null

• Nulls must be supported in algebra

• ? (? (B, copies), copies (publ, pages, date)) = B

• ?, ? inverses iff S ? N
  • S is set of scalar fields
  • N is set of non-scalar fields
  • This is called PNF (partitioned normal form)

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