题目内容

维护阶段是软件生存周期中时间最长的阶段,也是花费精力和费用____的阶段。

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软件维护的工作流程是?

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简述统一建模语言UML的优点。

Operating systems for micro, mini, and mainframe computers perform many services. These services can be 1 either as “external” or “internal.” The operating system provides external services that help 2 start programs, manage stored data, and maintain 3 . You, as the computer user, control these external 4 . Using a command-line, menu-driven, or GUI user 5 , an operating system provides you with a way to select the 6 you would like to use. The operating system also helps you find, rename, and delete 7 and other data stored on disk or tape. On many, but not all computer 8 , the operating system helps you maintain security by checking your user ID and 9 , as well as protecting your data from 10 access and revisions.The 11 system provides internal services “behind the scenes” to ensure that the computer system functions 12 . These internal services are not generally under your control, but instead are controlled by the operating system itself. The operating system controls 13 and output, allocates system resources, manages the 14 space for programs and data, and 15 equipment failure without any direction from you.