Page 452 - Computer_Science_F5

Example 8.1 (iii) The entity Schedule may
Create the three data models from a
real-life scenario.
FOR ONLINE READING ONLY
Scenario: A route taken by a particular
bus company, whose buses travel
according to a given schedule.
Step 1: Creating a conceptual data
model
In this step, you have to identify
entities and their relationships.
There are three entities, which are:
Route, Bus Company, and Schedule.
Concerning relationships, one route
can have one or many bus companies
offering transportation services to
passengers. Also, a route can have one
or multiple transportation schedules.
Step 2: Creating a logical data model
Identification of characteristics,
primary keys, and foreign keys are
necessary for the establishment of a
logical data model in addition to the
names of entities and relationships
that were formed between entities in
step 1.
(a) Identification of attributes
(i) The entity Route may have
the following attributes: route
number, route name, origin,
and destination.
(ii) The entity Bus Company may
have the following attributes:
company id, route number,
owner name, and postcode.
443
Student’s Book Form Five
Computer Science Form 5.indd 443
have the following attributes:
schedule number, route
number, departure time, and
arrival time. Chapter Eight: Databases and Database Management Systems
(b) Primary keys
Under the current scenario, the
primary keys are route number,
company ID, and schedule number
for entities Route, Bus Company,
and Schedule, respectively.
(c) Foreign keys
According to the relationships
established in Step 1, the route
number from the entity Route
will become a foreign key in the
remaining entities, which are Bus
Company and Schedule. This
implies that there shall be an
addition of one attribute (route
number) in the Bus Company and
Schedule entities.
Step 3: Creating a physical data
model
The creation of the physical data
model requires defining the names
of the tables, names of the columns,
and column data types in addition to
the characteristics, primary key, and
foreign keys described in the logical
data model in step 2. Since the physical
data model is also an implementation
of the database, its specification may
be dependent on a particular database
management system such as MS
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