Previous NextView PDF6 Data Dictionary and Dynamic Performance Views Previous NextView PDF 第6章数据字典和动态性能视图This chapter describes the central set of read-only reference tables and views of each Oracle database, known collectively as the data dictionary. The chapter also describes the dynamic performance views, which are special views that are continuously updated while a database is open and in use. 本章介绍了每个 Oracle 数据库都具有的只读参考表和视图中最重要的部分，统称为数据字典。
本章还介绍了动态性能视图，它们是一些会在数据库处于打开状态时不断更新的特殊视图。
This chapter contains the following sections: 本章包含以下各节：∙Overview of the Data Dictionaryo Contents of the Data Dictionaryo Storage of the Data Dictionaryo How Oracle Database Uses the Data Dictionary ∙Overview of the Dynamic Performance Viewso Contents of the Dynamic Performance Viewso Storage of the Dynamic Performance Views∙Database Object Metadata ∙数据字典概述o数据字典的内容o数据字典存储o Oracle数据库如何使用数据字典∙动态性能视图概述o动态性能视图的内容o动态性能视图的存储∙数据库对象元数据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: Oracle 数据库的一个重要部分是它的数据字典，它是一组提供有关数据库管理元数据的只读表。
数据字典包含如下信息：∙The definitions of every schema object in the database, includingdefault values for columns and integrity constraint information∙在数据库中每个模式对象的定义，包括列的默认值和完整性约束信息∙The amount of space allocated for and currently used by theschema objects∙分配给模式对象的空间量及当前已使用量∙The names of Oracle Database users, privileges and roles granted ∙Oracle数据库用户的名称、授予用户的权限和角色、和与用户相关to users, and auditing information related to users (see "UserAccounts")的审计信息（请参阅"用户帐户"）The data dictionary is a central part of data management for every Oracle database. For example, the database performs the following actions: 数据字典是每个 Oracle 数据库数据管理的核心部分。
例如，数据库执行下列操作：∙Accesses the data dictionary to find information about users,schema objects, and storage structures∙访问数据字典来查找有关用户、模式对象、和存储结构的信息∙Modifies the data dictionary every time that a DDL statement is issued (see "Data Definition Language (DDL) Statements") ∙每次发出 DDL 语句时，修改数据字典（请参见"数据定义语言(DDL) 语句"）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. 就像存储其他数据一样，数据库将数据字典数据存储在表中，用户可以使用SQL来查询其中的数据。
例如，用户可以运行 SELECT 语句，以确定他们的权限，在他们的模式中有哪些表，这些表中有哪些列，这些列上是否建有索引等。
See Also: 另见："Introduction to Schema Objects""模式对象介绍"Contents of the Data Dictionary 数据字典的内容The data dictionary consists of the following types of objects: 数据字典包含下列类型的对象：∙Base tables ∙基表These underlying tables store information about the database. Only Oracle Database should write to and read these tables. Users rarely access the base tables directly because they are normalized and most data is stored in a cryptic format. 这些基础表存储有关数据库的信息。
只应该由数据库写入和读取这些表。
用户很少直接访问基础表，因为他们已被规范化，且大多数数据存储为一种神秘的格式。
∙Views ∙视图These views decode the base table data into useful information, such as user or table names, using joins and WHERE clauses to simplify the information. These views contain the names and description of all objects in the data dictionary. Some views areaccessible to all database users, whereas others are intended foradministrators only. 这些视图通过使用联接和 WHERE 子句来简化信息，将基础表的数据解码成有用的信息（如用户或表名等）。
这些视图包含数据字典中的所有对象的名称和描述。
一些视图可以被所有数据库用户访问，而其他一些则仅供管理员访问。
Typically, data dictionary views are grouped in sets. In many cases, a set consists of three views containing similar information and distinguished from each other by their prefixes, as shown in Table 6-1. By querying the appropriate views, you can access only the information relevant for you. 通常，数据字典视图按集合分组。
在许多的情况下，一个集合由三个包含相似信息的视图，并且彼此之间通过不同的前缀来区分，如表 6-1 中所示。
通过查询相应的视图，您可以访问只与您相关的信息。
Table 6-1 Data Dictionary View Sets 表 6－1 数据字典视图集Prefix UserAccess Contents Notes 前缀用户访问内容注意DBA_Databaseadministrators All objects Some DBA_ views have additionalcolumns containing information usefulto the administrator.DBA_数据库管理员所有对象一些 DBA_ 视图具有更多的列，其中包含对管理员有用的信息。
ALL_All users Objects towhich userhasprivileges Includes objects owned by user. Theseviews obey the current set of enabledroles.ALL_所有用户用户具有访问权限的对象包括用户所拥有的对象。
这些视图服从当前已启用的角色集合。
