Computer Science Centre University of Indonesia Chapter 3 Data
Modelling Using Entity-Relationship (ER) Model Slide 2 Phases of
Database Design Slide 3 Company Example Database Application
Description of the mini-world: The company is organized into
departments. Each department has a unique name, a unique number and
a particular employee who manages the department, including the
date he/she began managing the department. A department may have
several locations. Slide 4 Contd A department controls a number of
projects Each project has a unique name, number and a single
location Slide 5 Contd We record each employees name, SSN, address,
salary, sex and birth date. Also we record who is the supervisor An
employee works in one department but may work on several projects
in different department We track work hours of employees in
projects Slide 6 Contd We record the dependants of each employee,
including the first name, sex, birth date and relationship to the
employee Slide 7 ER Schema for Company Slide 8 Entity &
Attributes Entity is the thing either physical existence (person,
car, house) or conceptual (company, course, job). Attributes are
the properties of the entity Each attributes has values. Slide 9
Entity, attribute & value example Slide 10 Composite vs. Simple
Attributes Composite attributes can be divided into smaller part.
For example, address consist of Street Address City State Postal
Code Simple (atomic) attributes are no longer divisble Slide 11
Cond Slide 12 Single valued vs. Multi-valued Singe valued: Age Sex
SSN Multi valued: Children Slide 13 Other terms Stored vs. derived
values. Derived values example may include GPA, sub- totals, etc.
Null values: nothing, not zero, not blank space! Slide 14 Complex
attributes Composite and multi-valued attributes can be nested in
an arbitrary way () for nesting {} for multi value Example
{Address&Phone ( {Phone(AreaCode, PhoneNumber)},
Address(StreetAddress(Number, Street, ApartmentNumber), City,
State, Zip) ) } 1850 b"> Value Sets Possible values of an
attribute. Usually: Numeric Text Boolean Etc. But can be more
specific, for example: Birth date must be > 1850 but before
