Describe the Tables that are part of the Data Dictionary
Data Dictionary Tables
The data dictionary[1] will contain several tables listing the tables, columns, indexes, and permissions comprising the database. The following two MouseOvers show the first few rows of two tables in a data dictionary. The first, SYSCATALOG, lists the tables in the database.
Creator column: The Creator column shows which user created a table.
TName column: The Tname column contains the names of the tables in the database.
DBSpace: The DBSpace column shows where each table is stored on the computer.
TableType: The TableType column shows the type of each table (e.g., base table, temporary table).
Ncols: The number of columns in a table.
PrimaryKey: Whether the table has a primary key field or fields.
View the diagram below to learn more about SYSCOLUMNS characteristics.
SYSCOLUMNS characteristics
SysCol Table
The second, SYSCOLUMNS, lists the characteristics of every table column in the database.
The next lesson wraps up this module.
Metadata
Metadata about the actual data structures themselves should be able to be selected from system tables, usually called system catalogs. For example, in Oracle these tables make up the Oracle Data Dictionary. These catalogs or library tables contain the key pieces of data about the Physical model in data element form. Some even store the definitions of the tables and columns. This emphasizes that the data model and database structures are
available for public use.
[1]data dictionary: A list of descriptions of data items to help developers stay on the same track.