DATABASE DEVELOPMENT LIFE CYCLE - Database Design and Development: An Essential Guide for IT Professionals - page 95

Requirements Analysis and Design Storage allocations Application testing Production

Semantic
modeling

Physical
design

Model
transformation

Figure 4-3 Database design and development.

loan account. Is your organization a medical center? Then a few of its entities are
patient, physician, diagnosis, and treatment procedures. Whatever the nature of your
organization's core business, you list the business entities and determine the infor-
mation desired about each of these entities. In the case of the banking institution,
a customer is related to one or more checking accounts. While considering the busi-
ness entities, you note such relationships between sets of entities. These relation-
ships must be ascertained to understand how information will be retrieved from the
database system and used.
Let us say that you have determined the entities and the relationships. What do
you do with them? How do you represent them in the database, and how do you
store information about them? How do you design your database system? Design
is broken down into two phases based on what actually happens in the design
process itself.

Logical Design. True, data is stored in the database as files and records. But what
about the structure of the data? What are the pieces of data within each structure?
How do the various elements of the structure relate to one another? What are the
connections? In the first design phase, you formulate these data structures, their
arrangement, and their relationships. You come up with the conceptual view of the
database. You use boxes and lines to represent this conceptual view as a logical
design diagram. This design is not at the level of how data is stored as files, records,
and fields. It is at a higher level that can be understood easily by the users—a level
that can be used as a means for communication among the database practitioners
and between the database practitioners and the user groups.

Physical Design. Once the logical design is firmed up, it has to be transformed
into the design of the physical files and records because that is how data can be in