PHYSICAL DATABASE DESIGN - Fundamentals of Database Management Systems - page 220

Data Volume Assessment How much data will be in the database? Roughly, how
many records is each table expected to have? Some physical design decisions will
hinge on whether a table is expected to have 300, 30,000, or 3,000,000 records.
Data Volatility Data volatility describes how often stored data is updated. Some
data, such as active inventory records that reflect the changes in goods constantly
being put into and taken out of inventory, is updated frequently. Some data, such
as historic sales records, is never updated (except for the addition of data from
the latest time period to the end of the table). How frequently data is updated, the
volatility of the data, is an important factor in certain physical design decisions.
Application Characteristics
The nature of the applications that will use the data, which applications are the most
important to the company, and which data will be accessed by each application form
yet another set of inputs and factors in physical design.
Application Data Requirements Exactly which database tables does each application
require for its processing? Do the applications require that tables be joined? How
many applications and which specific applications will share particular database
tables? Are the applications that use a particular table run frequently or infrequently?
Questions like these yield one indication of how much demand there will be for
access to each table and its data. More heavily used tables and tables frequently
involved in joins require particular attention in the physical design process.
Application Priorities Typically, tables in a database will be shared by different
applications. Sometimes, a modification to a table during physical design that's
proposed to help the performance of one application hinders the performance of
another application. When a conflict like that arises, it's important to know which
of the two applications is the more critical to the company. Sometimes this can be
determined on an increased profit or cost-saving basis. Sometimes it can be based
on which application's sponsor has greater political power in the company. But,
whatever the basis, it is important to note the relative priority of the company's
applications for physical design choice considerations.
Operational Requirements: Data Security, Backup, and Recovery
Certain physical design decisions can depend on such data management issues as
data security and backup and recovery. Data security, which will be discussed in
Chapter 11, can include such concerns as protecting data from theft or malicious
destruction and making sure that sensitive data is accessible only to those employees
of the company who have a ''need to know.'' Backup and recovery, which will also
be discussed in Chapter 11, ranges from recovering a table or a database that has
been corrupted or lost due to hardware or software failure to recovering an entire
information system after a natural disaster. Sometimes, data security and backup
and recovery concerns can affect physical design decisions.
Hardware and Software Characteristics Finally, the hardware and software
environments in which the databases will reside have an important bearing on
physical design.