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Mapping Rules (cont)

Selection:

SELECT   ...   FROM   ... R ...   WHERE  ... R.f  op  val ...

⇒    Select[R.f op val](R)

SELECT   ...   FROM   ... R ...   WHERE  ... Cond1,R  AND  Cond2,R ...

⇒    Select[Cond1,R & Cond2,R](R)
or
⇒    Select[Cond1,R](Select[Cond2,R](R))