Databases Reference
In-Depth Information
methodology encourages comprehensive understanding of business
information requirements by suggesting a cookbook-like approach com-
plete with steps, rules, and implementation tips. It should enable even an
inexperienced analyst to tackle complex design problems with confi-
dence. Third, it facilitates effective communication among designers,
developers, and users throughout the design process. The methodology
relies heavily on diagramming techniques to illustrate information and
relationships more clearly and concisely than textual descriptions alone
can do. Finally, the methodology contributes to designing optimal data-
bases using any database technology. In fact, because of the data-driven
(technology-independent) nature of the methodology, a data model can be
built even before deciding on a database environment.
Optimal database design is:
•
Correct —
It provides an accurate and faithful representation of the
way information is used in the business.
•
Consistent —
It contains no contradictions in the way the information
objects are named, defined, related, and documented.
•
Sharable —
It is accessible by multiple applications and users to meet
varying access requirements.
•
Flexible —
It facilitates additions to reflect new information require-
ments, tweaking to accommodate strengths or weaknesses of a partic-
ular implementation approach, and modifications to respond to
changes in business operations.
Many approaches and methodologies can be used for data modeling;
some are more formal and more intimidating than others. The methodol-
ogy described in this chapter is not so much formal as practica21l — that
is, it is a simplified version of a rigorous, formal treatment. The combina-
tion of simplicity and practicality makes it effective for the modeling
requirements of many business situations.
MAJOR CONCEPTS OF DATA MODELING
Exhibit 1 shows a very simple data model of Ron's Real Estate Business.
Even knowing nothing about data modeling, by looking at Exhibit 1 it is
obvious that:
• Ron deals with renters, properties (beach and mountain), and rental
agreements. These seem to be the most important objects or concepts
(or entities) in the exhibit.
• Renters rent rental agreements, and properties are rented to rental
agreements. In addition, there are beach properties and mountain
properties. The arrows reflect associations (relationships) between
the boxes (entities).
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