DATABASE DEVELOPMENT LIFE CYCLE - Database Design and Development: An Essential Guide for IT Professionals - page 96

physical storage. Each component of the logical design is mapped into one or more
physical design components. Physical design deals with data storage, data retrieval,
data updates, and methods for improving data access performance. Where you want
to keep the data, how you intend to lay out the data on the storage media, how you
establish the relationships at the storage level—these make up the components of
the physical design.

Development and Implementation

When the logical design and physical design phases are completed, you are ready
to develop and implement the database. The database administrator has the respon-
sibility of completing the development and implementing the database. He or she
defines the data structures, relationships, business rule constraints, storage areas, and
performance improvement techniques in the data dictionary.
The database is then populated with data. If the transition in an organization is
from a file-oriented system to a database system, then data from the previous files
are extracted and converted. Special database utility programs and specially written
conversion programs are used to load data in the new database.

Steps and Tasks

The life cycle approach comprises systematic and well-defined steps or phases to
complete the design and development of a database system. Each step comprises
specific major activities; each activity contains individual tasks. Although the project
progresses from step to step, it is not necessary to complete all the activities of one
step to proceed to the next. Parts of the steps may be performed in parallel. Some-
times it becomes necessary to repeat and refine some of the steps in an iterative
manner.
Figure 4-4 shows the major steps of the database development life cycle (DDLC).
Note the sequence of the steps from the bottom to the top. Note how the figure
illustrates that the steps may be performed in parallel. While some aspects of
requirements definition are still to be completed, the design step may commence.
Also, observe the indication of the iterative nature of design and develop-
ment. When you complete a portion of the design, you may want to go back to
the requirements definition phase to review and refine a few aspects of the data
requirements.

MAINTENANCE & GROWTH

IMPLEMENTATION & DEPLOYMENT

DESIGN

ITERATIVE

REQUIREMENTS DEFINITION

FEASIBILITY STUDY

PLANNING

Figure 4-4 DDLC: major steps or phases.