- Recall:
mapping a
conceptual schema to
an external schema:
- $64,000 question:
- Suppose the
conceptual schema
changes....
- Can we still obtain the (old) external schema (assuming we have all the necessary information in the conceptual schema)
- Suppose the
conceptual schema
changes....
- Logical data independence:
- Logical data independence =
the ability to
present
the data stored in a
conceptual schema format
in any way
required (desired) by the user.
In other words:
- We can map the conceptual schema to any external schema (assuming we have all the necessary information in the conceptual schema)
- Logical data independence =
the ability to
present
the data stored in a
conceptual schema format
in any way
required (desired) by the user.
- Logical Data Independence will
enable us to:
- change
the way (= structure) we store the data
in the conceptual schema
and
- still be able to present the data in the same way (external schema) to the user !!!!
Schematically:
- change
the way (= structure) we store the data
in the conceptual schema
and
- Important fact:
- A well-designed
database model can
provide
Logical Data Independence
(You have seen how it is done, but you will need to learn SQL to fully understand the "how".)
- A well-designed
database model can
provide
Logical Data Independence
-
Why is
Logical Data Independence such
a big deal:
- Data to the end user is
not just a
file that he/she
looks (stares ?) at !!!
- The end user may have
their own
applications
that perform
further processing
(One such application is Excel !!!)
- The data analysis tools (programs)
used by the end user
requires a
specific data format
(Or else, the end user cannot import the data into their tool ofr further analysis !!!)
- The data analysis tools (programs)
used by the end user
requires a
specific data format
- The end user programs
requires that the
format of the data be
unchanged in the event
that the Conceptual Scheme
is updated !!!!
(Or else, the end users will have to change the way they import the data !!!)
- The Logical Data Independence
technique can maintain the
end user data file structure
in the same format
It will make end users very happy customers !
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