数据库系统的三级模式分别为 模式、内部级模式与外部级模式。
参考答案：概念或概念级
解析：[评析] 数据库系统在其内部具有三级模式及二级映射，三级模式分别是概念级模式、内部级模式和外部级模式。概念模式是数据库系统中全局数据逻辑结构的描述，是全体用户(应用)公共数据视图。内模式又称物理模式，它给出了数据库物理存储结构与物理存取方法，如数据存储的文件结构、索引、集簇及hash等存取方式与存取路径，内模式的物理性主要体现在操作系统及文件级上，它还未深入到设备级上(如磁盘及磁盘操作)。外模式也称子模式或用户模式，它是用户的数据视图，也就是用户所见到的数据模式，它由概念模式推导而出。
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| A good dictionary is 1 important tool (工具). It will tell you 2 only what a word means but 3 how it 4 . A dictionary needs to be printed again about every ten years. Languages develop (发展) and a good dictionary must 5 these new changes. A new English dictionary will only tell you 6 most people use the language today. It will not tell you what is right 7 wrong. It may tell you the right time to use a word. If only 8 people use a word, a dictionary will 9 tell you this or not list (编列) it. 10 dictionary will tell you many interesting facts. If you type (用打字机打) a word and the word is too long, 11 in your dictionary. All dictionaries show you 12 to break (拆开) a word. And they also show you how a word 13 . Every dictionary, of course, tells you what a word means. But some words, like "get" or "take", may have lots of meanings (意思). In some dictionaries, the main (主要的) meanings are often listed first. In 14 , the newest meanings are listed last. So before you use your dictionary, you should always 15 the front part. This part explains 16 . Some dictionaries also show you where a word comes 17 . Do you know that the word "brand" (标记) comes from an old word? This old word means "to burn". This is because 18 years ago people burned their names on tables or boats to show who 19 them. They also burned their own names on their farm animals 20 they would not be stolen. Your dictionary also has a lot of other interesting facts in it. After you have learned to use a dictionary, it can become your best useful book. |
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