About the concept of a database dictionary __ database

In database design, the term "database dictionary" is involved in the discussion with colleagues. Since it was not DBA origin, the concept was not fully understood in the previous database design, so the discussion was somewhat confusing and always felt plausible. I searched the internet for some details.

http://zh-cn.tech-faq.com/data-dictionary.shtml sources of information.

What is a data dictionary.

A data dictionary is a reserved space database that is used to store information about the database itself.

Information that may be contained in a data dictionary, such as: Database design data stored SQL program user Rights user statistics database process information Database performance statistics

See here, it is more clear, and then refer to http://jonescheng.javaeye.com/blog/183638, from which the data dictionary of different databases has its own definition of the way. The contents are as follows:

understand what a data dictionary is and what a data dictionary is

Each Oracle database includes a collection called "metadata," or contains data that describes the database data structure. The tables and views that contain these metadata are called Oracle data dictionaries.
Tables with prefixes v$ or gv$ in the data dictionary are dynamic tables that are constantly updated to reflect the current state of the Oracle database. static data dictionary tables have a prefix, such as Dba_, All_, or user_, that represents the range of objects listed in the view.

Tables and views in the database component database dictionary
Database V$database
Table Space Dba_tablespace,dba_data_files,
Dba_free_space
Control file V$controlfile,v$parameter,
V$controlfile_record_section
Data File V$datafile,v$datafile_header,v$filestat,
Dba_data_files
Duan Dba_segments
Data range Dba_extents
Log threads, log groups, and V$thread,v$log,v$logfile
Log sequence Number
Archive status V$database,v$log,v$archived_log,
V$archive_dest
Database Instance V$instance,v$parameter,
V$system_parameter
Memory Structure V$sga,v$sgastat,v$db_object_cache,v$sql,
V$sqltext,v$sqlarea
Background process V$bgprocess,v$session

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The data dictionary is a text block that describes the field name, field length and field description of the table in the database.
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A data dictionary is a description of a field in a database, stating
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A data dictionary is a collection of basic elements that are stored in a database. It can store the basic table data structure, stored procedures, etc. ...
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A data dictionary is a table that records information about certain databases.
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Each programming environment has two basic components: The program logic-the job description that the program needs to do-and the data. You can temporarily save data, such as a file or database, within a program, or in a persistent and externally variable manner. The traditional file structure requires the developer to understand and then describe the file structure so that the program can access it appropriately and process the fields or records of the file. However, within an Oracle relational database, the entire database structure (including its tables, views, indexes, users, security rules, and so on) is stored in a special set of tables and views, called the data dictionary.

The Oracle data dictionary is owned by a special user account and is called Sys. The SYS account is the same as the root superuser of the Unix system. Typically, developers will never need to connect to a shared database as a privileged account. The database administrator is not even encouraged to use the SYS account for any work, but there are few operations that require that level of capability. If you are both a developer and a DBA, perhaps in the personal replication of an Oracle database, you need to understand the potential crisis of interactive work as a connection to Sys.

Another generic entry on the Oracle data dictionary stores its tables in special tablespaces (such as system and Sysaux). In these special tablespaces, you never create additional application database objects.

The key to an Oracle data dictionary is that you can access the application's data structure within the database using the same SQL language. Typically, a direct access dictionary is limited to a SELECT statement (never publish Insert, UPDATE, or DELETE statements against a Dictionary object). The data dictionary is modified indirectly through a special SQL statement, which is usually referred to as the data Processing language (DML) command. DML statements, such as Create TABLE, DROP INDEX, Grant, and so on, require special permission. They are typically executed by DBAs in the development Organization, which allocates responsibilities between DBAs and developers. In order to establish and maintain your own database environment, students or developers who work independently will have to learn SLQ DML commands.



Concepts in the data dictionary in SQL Server

The data dictionary is divided into two categories:
The definition of the system field is recorded in a DBMS in some of the SYS tables in SQL, and the stored procedure of the relational trigger view ...

Second, the user's data dictionary is equivalent to the processing of the system above and the user object description and management, etc.

Information about the various objects in the database, such as
Dbo.syscolumns Records table columns, parameters in stored procedures, columns in index
Dbo.syscomments create statements that record stored procedures, views, and so on
Dbo.sysdepends records the dependencies between objects
Dbo.sysfilegroups records the file group information
Dbo.sysfiles Record Data file information
Dbo.sysfiles1 .....
Dbo.sysforeignkeys Record foreign key information
Dbo.sysfulltextcatalogs Information for Full-text indexing
Dbo.sysfulltextnotify .....
Dbo.sysindexes Records index and related table information
Dbo.sysindexkeys .....
Dbo.sysmembers .....
Dbo.sysobjects Log all database objects
Dbo.syspermissions
Dbo.sysproperties
Dbo.sysprotects
Dbo.sysreferences
Dbo.systypes records all data types in the database
Dbo.sysusers records information for all users in the database