THE PHYSICAL DESIGN PROCESS - Database Design and Development: An Essential Guide for IT Professionals - page 347

within files. How do you map relations, columns, and rows to files and records? Do
you store one relation per file? Or is it more efficient to store several relations in
one computer file? Are there advantages if you intend to store related rows from
two relations in one file? What happens when the database system grows in size and
more transactions begin to access the system? Decisions such as these make up the
physical design process. We will consider all the relevant issues and describe the
goals and tasks of physical design.
Goals and Design Decisions
Of course, the main objective of physical design is the implementation of the logical
design on physical storage. Only then can you begin to store data in the target data-
base and provide for its usage by users. Although this objective appears to be
straightforward, when designing the data structures to be stored you need to be
concerned with certain crucial issues.
If the way you store data in storage makes data retrieval cumbersome and inef-
ficient, your physical design lacks quality and usefulness. If your data storage
method is not compatible with the features of the host system and is difficult for
the target DBMS to work with, then again your physical design becomes ineffec-
tive. Therefore, let us consider the main goals and decision issues.
Physical Design Goals Two major goals stand out for the physical design
process. All tasks must be conditioned to achieve these goals.
Database performance. Your physical design must ensure optimal performance.
This means, as data are retrieved from storage, retrieval must be as fast as possible.
Again, when a piece of data is written on storage, it must be done as quickly as
possible. Fast data operations constitute a major goal. In terms of physical storage,
this translates into minimizing the time for each input/output (I/O) operation. This
concern for database performance must continue as usage intensifies after the initial
deployment. The physical design must be open and flexible to accommodate all
future adjustments for continued better performance.
Data management. As data are stored in your database systems and begin to be
used, you now have a vital resource to be managed well and protected. Your phys-
ical design must enable effective management of the database. This may involve
grouping of tables to be managed as a collection for the purpose of backup and
recovery. This may require setting up of proper data views for individual user groups
and protecting the database from unauthorized usage.
In addition to the two major goals of database performance and data manage-
ment, let us list a few other underlying objectives in the physical design process.
Consider the following:
Scalability. As the usage of the database system continues to increase, you must
ensure that the physical design enables upward scalability of the system. When you
need to consider upgrades to hardware, operating system, and the DBMS itself, the
physical design must be able to adapt itself to the enhancements.