THE PHYSICAL DESIGN PROCESS - Database Design and Development: An Essential Guide for IT Professionals - page 348

Openness and flexibility. Business conditions do not stay static but keep changing
all the time. What happens when business conditions change? These changes must
be reflected in your database system so that it can support business operations ade-
quately. On the basis of the changes, the logical data model will change and evolve.
How should this affect the actual implementation of the database system? The phys-
ical design must be open and flexible enough to accommodate revisions to the
logical design.
Security. Safeguarding and protecting the database system from unauthorized
access is accomplished through the physical design. You must ensure that the
security features in the physical design provide thorough and comprehensive
protection.
Ease of administration. Administrative details include database backup, recovery
from failures, and ongoing space allocation. The physical design must ensure easy
administration with simple and straightforward features.
Physical Design Decisions Initially and on an ongoing basis, the following
design issues require serious consideration and appropriate decisions:
• Features, functions, and options supported by the target DBMS
• Features and capabilities of host computer system
• Disk storage configuration
• Usage of data—access patterns and access frequencies
• Data volumes—initial volumes and growth rates
• Hardware and software—initial setup and ongoing upgrades
Physical Design Components
When you finish with the physical design phase, what collective set of com-
ponents do you expect to produce? At the end of physical design, what is the set
of components that are expected to emerge? What major components make up
the physical design of your database system? Here is a list of the essential
components:
File organization For each file in the physical model, the method or technique
for arranging the records of the file on physical storage
Indexes Types and list of index files to improve data access
Integrity constraints Constraints or rules in the form of data edit rules and busi-
ness rules; rules for enforcement of referential integrity on inserts and deletes
Data volumes Sizing for each data and index file
Data usage Analysis of expected data access paths and access frequencies
Data distribution Strategy for providing data to users by means of centralized,
partitioned, or replicated database systems