关于观点的问题 [英] question about views

问题描述

什么是观点？它与数据独立性有何关系？





单值属性和简单属性之间的区别

what is view? how it is related to data independence?


what is difference between single valued attribute and simple attribute

推荐答案

根据 wiki -



在数据库理论中，视图是存储查询的结果集数据，数据库用户可以像在持久数据库集合对象中一样查询数据。此预先建立的查询命令保存在数据库字典中。与关系数据库中的普通基表不同，视图不构成物理模式的一部分：作为结果集，它是在请求访问该视图时动态地从数据库中的数据计算或整理的虚拟表。应用于相关基础表中数据的更改将反映在后续视图调用中显示的数据中。在某些NoSQL数据库中，视图是查询数据的唯一方法。 了解更多...... [ ^ ]



A 单值属性是一个只能有一个值的人。例如，一个人只有一个名字，只有一个社会安全号码。



简单属性是一个无法分解为它的组成部分。例如，一个人的性别被分类为M或F，并且没有合理的方法来分解M或F.同样，一个人的名字不能被分解为有意义的组成部分。



-KR

As per wiki -

In database theory, a view is the result set of a stored query on the data, which the database users can query just as they would in a persistent database collection object. This pre-established query command is kept in the database dictionary. Unlike ordinary base tables in a relational database, a view does not form part of the physical schema: as a result set, it is a virtual table computed or collated from data in the database, dynamically when access to that view is requested. Changes applied to the data in a relevant underlying table are reflected in the data shown in subsequent invocations of the view. In some NoSQL databases, views are the only way to query data. see more...[^]

A single-valued attribute is one that can have only one value. For example, a person has only one first name and only one social security number.

A simple attribute is one that cannot be decomposed into its component pieces. For example, a person's sex is classified as either M or F and there is no reasonable way to decompose M or F. Similarly, a person's first name cannot be decomposed into meaningful components.

-KR

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