The Iterator Model

• Execution begins at root

  • open, getNext, close
  • Propagate calls to children
    Non-pipelined operation may require multiple getNexts
    

• Efficient scheduling & resource usage

• Poor if slow sources (getNext may block)

SelectClient = “Atkins”

JoinPressRel.Symbol = Clients.Symbol

Scan

PressRel

Scan

Clients

JoinSymbol = Northwest.CoSymbol

ProjectCoSymbol

ScanNorthwest

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