Database Reference
In-Depth Information
The System Catalog
Every reputable DBMS contains a system catalog (also called the data dictionary) of some
form. This has been alluded to several times earlier in the course. This chapter discusses
this very important component of the database system. The chapter proceeds under the
following subtopics:
•
Introduction
•
Three Important Catalog Tables
•
Other Catalog Tables
•
Querying the System Catalog
•
Updating the System Catalog
•
Summary and Concluding Remarks
14.1 Introduction
The system catalog (data dictionary) is perhaps the most important database object in
a database system. This is so because it facilitates and supports all or most of the other
database objects. The system catalog typically contains
metadata
about the database.
By metadata, we mean data about other data. This catalog itself consists of relational
tables, which can be manipulated using SQL statements. The system catalog provides the
following benefits:
•
The system catalog, by maintaining metadata in the form of other
relational tables, facilitates most (if not all) of the other database
objects. This fulfills the requirements of the Zero Rule of Chapter 9.
•
Through the system catalog, the DBMS is able to deliver on
the requirements of physical and logical data independence
(Chapters 1 and 9) in a sleek manner.
•
Through the system catalog, the DBMS is able to deliver on the
requirement of integrity independence (Chapters 4, 5 and 9).
