Most of the data dictionary is constructed in a matrix fashion. The first way to categorize data dictionary views is by the breadth of information they cover. Views can be divided into four groups:
Views that allow you to see objects you own. Most of these views begin with USER_.
Views that allow you to see objects that you own or that were granted to you. Most of these views begin with ALL_.
Views that allow you to see all objects in the database. These are primarily for use by the DBA. Most of these views begin with DBA_.
A handful of other views that provide information of general interest about the database.
The second way to categorize data dictionary views is by content. Many of the USER_, ALL_, and DBA_ views are grouped in families, according to how their view names end (e.g., TABLES, COLUMNS, and so on). Groups of views provide information about various topics, including:
Tables
Storage
Columns
Views
Objects
Networking objects
As this is a book for DBAs, in this chapter we’ll concentrate on the DBA_ views and the other views of interest to DBAs. The ALL_ views have the same structure as the DBA_ views. The USER_ views have the same structure as the DBA_ views with the exception that they do not include the OWNER column.