Introduction - Database Processing: Fundamentals, Design, and Implementation - page 13

USER_TABLES Table

Figure 1-13
Generic Metadata tables

TableName NumberColumns PrimaryKey

STUDENT 4 StudentNumber

CLASS 4 ClassNumber

GRADE 3 (StudentNumber, ClassNumber)

USER_COLUMNS Table

ColumnName TableName DataType Length (bytes)

StudentNumber STUDENT Integer 4

LastName STUDENT Text 25

FirstName STUDENT Text 25

EmailAddress STUDENT Text 100

ClassNumber CLASS Integer 4

Name CLASS Text 25

Text

Term CLASS 12

Section CLASS Integer 4

StudentNumber GRADE Integer 4

ClassNumber GRADE Integer 4

Grade GRADE Decimal (2, 1)

By The Way Because metadata is stored in tables, you can use SQL to query it, as just
illustrated. Thus, by learning how to write SQL to query user tables, you
will also learn how to write SQL to query metadata. To do that, you just apply the SQL
statements to metadata tables rather than user tables.

In addition to user tables and metadata, databases contain other elements, as shown in
Figure 1-14. These other components will be described in detail in subsequent chapters. For
now, however, understand that indexes are structures that speed the sorting and searching
of database data. Triggers and stored procedures are programs that are stored within the da-
tabase. Triggers are used to maintain database accuracy and consistency and to enforce data
constraints. Stored procedures are used for database administration tasks and are sometimes
part of database applications. You will learn more about these different elements in Chapters 7,
10, 10A, 10B, and 10C.
Security data define users, groups, and allowed permissions for users and groups. The
particulars depend on the DBMS product in use. Finally, backup and recovery data are used