Introduction to NonStop SQL/MP

Physical Database Structure
NonStop SQL Architecture
3–2 113425 Tandem Computers Incorporated
Figure 3-1. Database Structure
TABLENAME
Database Table Catalog Table
TABLES Table
EMPLOYEE Table
1
23
29
•••
ROGER
JERRY
JANE
•••
GREEN
HOWARD
•••
EMPNUM
FIRST_NAME LAST_NAME •••
•••
•••
•••RAYMOND
Logical Level
•••
\SYS1.$VOL1.PERSNL.EMPLOYEE
•••
TABLENAME
File Label
EMPLOYEE
File
Physical Level
$VOL1 Disk
Volume
Contains EMPLOYEE File Name
and Location, Name of Catalog
Table Describing the File, and
Other Information
Physical Data
Although Figure 3-1 shows only one file, a single logical table can be partitioned over
many physical files.
As shown in Figure 3-1, a database table (or view) is defined logically in a set of entries
in catalog tables and is associated with one or more disk files. Each file has a file label
that describes its physical attributes such as its location on disk and the number of
extents. The file label also contains the names of the associated catalog tables as well
as catalog information about the logical structure of the object; thus, the physical and
logical structures are always synchronized.
Because the data dictionary resides in and describes both the logical and physical
structures, the dictionary is active—that is, whenever a change occurs in the physical
environment, the logical structure reflects that change.