ALLBASE/SQL Reference Manual (36216-90216)

Chapter 1 45
Introduction
ALLBASE/SQL Databases
created implicitly when you create objects that have a class name as owner name.
Refer to Chapter 2 , “Using ALLBASE/SQL,” in this manual and to the chapter “Logical
Design” in the ALLBASE/SQL Database Administration Guide for additional information
about authorization groups and classes.
To use data in a database, you need to specify the names of the tables and views you need.
You must also specify the owner name associated with the table or view unless you own it
(or you have used the ISQL SET OWNER command). When accessing the Composers table,
Wolfgang needs to specify only Composers. However, when accessing the quotas table, he
needs to specify Marketing.Quotas because Marketing owns the Quotas table.
You also need the proper authority to access data. An authority is a privilege given to a
user to perform a specific database operation, such as accessing certain tables and views
and creating groups or tables. ALLBASE/SQL uses authorities to safeguard databases
from access by unauthorized users. In the example above, before Wolfgang can access the
Quotas table, he must be granted the authority to do so by the owner of the table.
If you have been granted the proper authorization, you access databases by first
connecting to the DBEnvironment in which they reside:
CONNECT TO ' DBEnvironmentName '
Physical Concepts
Physically, the DBEnvironment is a collection of files for one or more logical databases.
A DBEFile is an MPE XL file. Most files in a DBEnvironment are DBEFiles. Data in the
tables of logical databases is stored in one or more DBEFiles. Indexes are also stored in
DBEFiles; an index is a structure that ALLBASE/SQL can use to quickly find data in a
table.
A DBEFileSet is a collection of DBEFiles. You associate physical storage with a
DBEFileSet by adding DBEFiles to the DBEFileSet. Each DBEFileSet can have more than
one DBEFile, but a single DBEFile cannot contain data for more than one DBEFileSet.
When you create a table, you can specify the DBEFileSet with which the table and its
indexes will be associated. This causes physical storage space for the table and indexes to
be allocated from the DBEFiles associated with the specified DBEFileSet. Figure 1-2.
illustrates the relationships among tables, DBEFiles, and DBEFileSets.