DATA MODELING BASICS - Database Design and Development: An Essential Guide for IT Professionals - page 142

methods to collect the information requirements to be implemented in the organi-
zation's database system. We have also indicated that these requirements drive the
design of the database system. So where does the data model fit in? Why do you
need to create a data model for the information requirements and to derive the
design from the data model?
In the Chapter 4, we discussed the logical design of a database system. The logical
design indicates the data structures and relationships; it shows how the various data
elements hang together and are perceived. In a relational database system, these
are perceived as two-dimensional tables. On the other hand, in a hierarchical data-
base system, these are reckoned as data segments arranged in a hierarchical, top-
down fashion. In a network database system, the arrangement is in the form of data
nodes connected to form a network.
The logical design for a relational database system shows the data structures as
tables, for a hierarchical database system as data segments, and for a network data-
base system as data nodes. The logical design indicates the structures according to
the conventional models—relational, hierarchical, or network. Now, see where the
generic data model fits in. It is the preliminary step in the logical design activity.
You create a generic data model that simply represents the real-world information
requirements without regard to the conventional model of the final, target database.
This step produces a replica of what real-world information must be found in the
final database, not necessarily according to any conventional model.
Creation of a generic data model as the preliminary step offers several benefits.
Here is a list of the major benefits:
• Provides independence so that any real-world information may be freely
represented without any restrictions from conventional models
• Captures the essence of the data structures
• Represents real-world objects and their data characteristics
• Defines how real-world objects are related
• Plain and simple representation; easily understandable
• Is at a basic level so that creation and refinement are easy
• Is a very effective method for data abstraction
Real-World Information Requirements
The term “real-world information” has been used a few times, and you may be won-
dering what exactly it means. Let us clarify. Information or data about the external
objects must be present in the database. The database is the internal representation
of the data about the external objects. These objects exist in the outside world or
the real world, whereas data about these objects exist inside the database. The data-
base residing inside a computer system, therefore, is the internal manifestation of
what exists outside in the real world.
Let us go back to the case of the university database. What does the internal uni-
versity database represent? It indicates the information requirements about the
objects present in the real world. What is the real world as far as the information
requirements for the university is concerned? What are the objects in this part of