tailieunhanh - oracle 8 database administration volume 1 instruction guide phần 5

Tham khảo tài liệu 'oracle 8 database administration volume 1 instruction guide phần 5', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Data Dictionary Structure Base Tables and Data Dictionary Views Data dictionary views - Views simplify the base table information - Created with the script Base tables - Normalized - Created with the script 5-4 Copyright Oracle Corporation 1998. All rights reserved. ORACLE The data dictionary located in the SYSTEM tablespace and owned by the user SYS contains two parts Base tables Data dictionary views Base Tables The foundation of the data dictionary is a set of base or underlying tables. The Oracle server writes and reads these tables. Database users rarely access them directly because they are normalized and the information is encoded. For example you would query the IND table to get information about the indexes that are defined in the database or select from the OBJ table to display the objects defined in the database. Never use DML commands such as INSERT UPDATE and DELETE to update the base data dictionary tables directly with the exception of the AUD table see the lesson Auditing . Oracle8 Database Administration 5-5 Lesson 5 Creating Data Dictionary Views and Standard Packages Data Dictionary Views The data dictionary views are created by running the script. These views decode and summarize the information in the base data dictionary tables. Public synonyms are created on the data dictionary views so that users can access them easily. Most users examine the data dictionary by selecting from the views rather than the base tables. 5-6 Oracle8 Database Administration Data Dictionary Structure Data Dictionary Views 5-5 Copyright Oracle Corporation 1998. All rights reserved. ORACLE Data Dictionary View Categories The data dictionary views are split into three categories. In many cases the views contain similar information and can be distinguished from each other by their prefixes. The Prefix USER These views are accessible by any user and generally refer to objects owned by a user for example USER_TABLES contains information on .