Databases Reference
In-Depth Information
Figure 3-2
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Logical Design
Physical Design
Conceptual Design
Data requirements
Information
requirements
Collection needs
Data locations
Logical framework
Applicable data
Data services
Data modeling
Physical modeling
Database objects
Object placement
Optimization
Logical design.
what the application needs to do. This is also where you identify the data require-
ments and collect the information you need. You aren't concerned about how
things will get done or which of the data you collect you actually need, you're
just pulling together everything you can find.
You start organizing the data during the
logical design
process (Figure 3-2).
This is where you sort through the data to identify what information applies to
the project and start putting together a basic logical framework. You identify the
basic type of database application that you need based on processing require-
ments. You start thinking about data services you'll need to support the appli-
cation. You also go back to the stakeholders for verification, to ensure that your
vision meets their expectations.
Data modeling occurs during logical design. During the process of data
modeling, you identify entities and attributes, distinguish relationships between
the entities, and make initial decisions about database tables. The framework is
still somewhat tentative at this point. You may find roadblocks to implementing
your design that force you to rethink and rework your logical framework.
Implementation details come in during
physical design
(Figure 3-3). The
focus moves from logical modeling to physical modeling. This is where you make
final decisions about how the data will be represented in the database. You've
already identified your attributes and now you decide how to store them. You
decide on the physical database objects that your solution will require. You
make decisions that will help you settle on a hardware platform, such as phys-
ical object placement, to optimize both space use and database performance. At
the end of this process you should have a complete physical design that you
will in turn use to install and configure your database server and create the
physical database.
Throughout the design process, it's important to realize that the conceptual,
logical, and physical design are all interrelated, and that you'll move back and
forth between them during the design process.
