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Made by AU and WEI WEI QIANG chap 1（5） Physical data independence 物理数据独立性： The ability to change the physical schema without changing the External schema is called physical data independence 应用程序如果不依赖于物理模式，它们就被称为是具有物理数据独立性 1.数据的物理独立性是指应用程序对数据存储结构的依赖程度。 2.数据物理独立性高是指当数据的物理结构发生变化时，应用程序不需要修改也可以正常工作。 logical data independence The ability to change the logical (conceptual) schema without changing the External schema (User View) 逻辑独立性是指用户的应用程序与数据库的逻辑结构是相互独立的，当数据的逻辑结构改变时，用户程序可以不变。 data model 书本p8 1.3.3 A conceptual tools to describe the data,data relationships,data semantics, and consistancy constraints 数据模型是数据特征的抽象，是数据库管理的教学形式框架。数据库系统中用以提供信息表示和操作手段的形式构架. 数据模型是描述数据、数据联系、数据语义以及一致性约束的概念工具的集合。 Data dictionary P21 1.8.1 Data dictionary, which stores metadata about the structure of the database, in particular the schema of the database. 数据字典：存储关于数据库结构的元数据，尤其是数据库模式 DML P9 1.4.1 data manipulation language A language for user to access or manipulate data as organised by the appropriate data model 全名：即数据操纵语言：用于表达数据库的查询和更新 chap 2(6) database schema The overall design of the database is called the database schema. 数据库的总体设计称作数据库模式。 relation instance the content of relation of given instance Aggregation (不肯定) Aggregation is an abstraction through which relationships are treated as higher-level entities. 聚集是一种抽象，通过这种抽象，联系被当做高层实体来看待。 聚集函数：输入值的一个集合，将单一值作为结果返回。 // atomic domain elements of the domain are considered to be indivisible units inner join natural join P57 a binary operation that allows us to combine certain selections and a Cartesian product into one operation. The natural join of r and s,denoted by r X s is,is a relation on schema R X S formally defined as follows 自然连接：二元运算，它使得我们可以将某些选择和笛卡儿积运算合并为一个运算 chap 3(2) view Any relation that is not part of the logical model,but is made visible to a user as a virtual relation 视图：任何不是逻辑 模型的一部分但作为虚关系对用户可见的关系称为视图。 // authorization 授权：将完成某项工作所必须的权力授给部属人员。 Specifying certain access rights to relations and views for certain user c