在编译程序时，采用的对中间代码的优化方法中，(30)是基于循环结构进行的优化处理。

①合并已知量

②删除归纳变量

③删除多余运算

④强度削弱

⑤复写传播

⑥代码外提

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The　relational　database　model　requires　the　data　be(71)through　programs　that　don't　rely　on　the　position　of　the　data　in　the　database.　This　is　in　direct(72)to　the　other　database　mode,　where　the　program　has　to　follow　a　series　of　pointers　to　the　data　it　seeks.　A　program(73)a　relational　database　simply　asks　for　the　data　it　seeks;　the　DBMS　performs　the　necessary　searches　and(74)the　information.　　The(75)on　how　the　search　is　done　are　specific　to　the　DBMS　and　vary　from　product　to　product.

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The　kernel　is　the(66)of　an　operating　system　such　as　Windows98,　Windows　NT,　Mac　OS　or　Unix.　The　kernel　provides　basic　services　for　the　other　parts　of　the　operating　system,(67)it　possible　for　it　to　run　several　programs　at　once(multitasking),　read　and　write　files　and　connect　to　networks　and　peripherals.　Applications　and　utility　programs　use　the　services　provided　by　the　kernel　to　provide　practical　business　functionality.

In　operating　systems　such　as　Windows　or　most　versions　of　Unix,　the　kernel(68)everything　except　application　and　utility　programs.

In　microkernel　operating　systems　such　as　Digital　Unix　and　Apples　forthcoming　Mac　OS　Server,　the　kernel(69)supports　only　multitasking　and　memory　management.　Other　services　such　as　applications,　utilities　and　the　user　interface　support　device　drivers,　API　and　graphics　which　all(70)outside　the　microkernel.