Overview of the Data Dictionary
数据字典概述
An important part of an Oracle database is its data dictionary, which is a read-only set
of tables that provides administrative metadata about the database. A data dictionary
contains information such as the following:
数据字典是Oracle数据库的重要组成部分，它是只读性表的集合，提供了用于管理数据库的元数据。数据字典包含如下信息：
■The definitions of every schema object in the database, including default values
for columns and integrity constraint information
数据库中，每一个方案对象定义信息，包括默认列值和完整性约束信息
■The amount of space allocated for and currently used by the schema objects
分配给方案对象及其当前已使用的空间信息
■The names of Oracle Database users, privileges and roles granted to users, and
auditing information related to users (see "User Accounts" on page 17-1)
Oracle数据库用户名称，授予用户的权限和角色，以及相关用户的审计信息
The data dictionary is a central part of data management for every Oracle database.
For example, the database performs the following actions:
数据字典是Oracle数据库数据管理的核心部分，例如，数据库执行以下操作：
■Accesses the data dictionary to find information about users, schema objects, and
storage structures
访问数据字典，查询用户、方案对象和存储结构信息
■Modifies the data dictionary every time that a DDL statement is issued (see "Data
Definition Language (DDL) Statements" on page 7-3)
每次执行DDL脚本，都会修改数据字典
Because Oracle Database stores data dictionary data in tables, just like other data,
users can query the data with SQL. For example, users can run SELECT statements to
determine their privileges, which tables exist in their schema, which columns are in
these tables, whether indexes are built on these columns, and so on.
像其他数据一样，Oracle数据库将数据字典数据存储在表里，用户可以用SQL查询这些数据。例如：用户可以执行SELECT语句查看自己的权限，方案中包含哪些表，表中包含哪些列，哪些列建有索引，等等。
