- Recall that
storing
duplicate information:
Name Course Course Name Semester Grade James Bond CS170 Intro to Computer Science Fall 1997 B- James Bond CS255 Assembler programming Fall 1998 B+ James Bond CS355 Computer Architecture Spring 1999 C+ John Doe CS170 Intro to Computer Science Spring 2000 A- John Doe CS255 Assembler programming Fall 2001 C+ John Doe CS355 Computer Architecture Spring 2002 D+ create an opportunity to have inconsistent information (when we update some but not all the information):
Name Course Course Name Semester Grade James Bond CS170 Intro to Computer Science Fall 1997 B- James Bond CS255 Assembler programming Fall 1998 B+ James Bond CS355 Computer Architecture Spring 1999 C+ John Doe CS170 Intro to Programming Spring 2000 A- John Doe CS255 Assembler programming Fall 2001 C+ John Doe CS355 Computer Architecture Spring 2002 D+
- What do we mean by
"designing a database":
- Recall
how a
database management system
satisfies the
need of
information to
its users:
- Fact:
we cannot control the
external schemas
--- they are defined by
their users
- We do
have control over the
conceptual schema:
- Recall
how a
database management system
satisfies the
need of
information to
its users:
- Very important fact:
- It is very important to
define a
conceptual model that:
- Can satisfy
all
the information needs
of the users
I.e.: we can map the conceptual schema to every external schemas used.
- Do not store
duplicate information
(Because this may cause data inconsistency)
- Can satisfy
all
the information needs
of the users
- It is very important to
define a
conceptual model that:
- Model design techniques:
- Model design technique = methodology used to define "good" conceptual models for a database system