Oracle's data dictionary consists of two parts: the data dictionary table and the data dictionary view. The basic table of the data dictionary is created by the file $ORACLE_HOME\RDBMS\ADMIN\sql.bsq. Most of the table names end with $, which belong to the sys user and are placed in the SYSTEM tablespace. The user cannot manually change the basic table of the data dictionary. Mine is in D:\oracle\product\11.2.0\dbhome_3\RDBMS\ADMIN\sql.bsq
Open the sql.bsq file to view the content (rem is a comment command), and drag to the bottom to see the file names, which means that the following files are executed when the sql.bsq file is executed.
For example, you can open dcore.bsq to view its contents. It creates the SYSTEM tablespace and data dictionary tables such as tab$ and obj$. tab$ displays the basic information of all tables in the database, and catalog.sql creates dynamic performance views (v_$ as a prefix) and synonyms.
The data dictionary package view contains three types: USER, ALL, and DBA. Which type of view has its view prefix, such as user_tables, etc. The beginning of USER indicates the view information that you own, the beginning of ALL indicates the view information that can be viewed with all your permissions, and the view information that can be viewed by the database administrator can be viewed at the beginning of DBA, and the view beginning with DBA can only be used by DBA users access.
You can query USER_VIEWS to see the view definitions owned by the user.
The dynamic performance view displays the activity status information, memory information and control file information of the database in the form of views. The view is usually prefixed with v_$, and the prefix v$ is a synonym for dynamic performance view. The database information that changes every moment is stored in the dynamic performance view. Not as good as v$parameter stores the values of all items in the initialization parameter file, v$process displays the current process information of the database, v$session current session information, v$lock lock information, v$transaction records transaction information, v$ logfile is about the location information of the instance reset log file, v$fixed_view_definition records the definition information of all dynamic performance views, etc.