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The diagram below shows the entity relationships for the database application.
(1,N)
Member
(1,N)
Rental
DVD
(1,1)
OnlineUser
4.2.1.1
Explanation of Entity Relationship Diagram
There are four tables shown in the entity relationship diagram above. Three of these tables
are related via a one-to-many (1,N) relationship. For instance the Member table has a 1:N
relationship with the Rental table, this means that a member can have many DVD’s on loan,
but a single DVD can only be loaned to one member at a time. The DVD table also has a 1:N
relationship with the Rental table. There is a 1:1 relationship between the Member and
OnlineUser tables, this means that no member has more than one login username and no
username is used by more than one member.
4.2.2
Normalisation
Normalisation is applied on data to ensure that a set of tables in the database are organized
efficiently. There are two main goals of normalisation, to eliminate any redundant data, so
the same data is not stored in more than one table and to ensure data dependency, by only
storing data related to that table. These goals reduce the amount of space a database
consumes and ensures that the data is logically stored.
I will normalise my database to third normal form, as this is sufficient for my application and
for the business as a whole. The definitions of the first three normal forms taken from [24]
are stated below.
First normal form (1NF) sets the very basic rules for an organised database:
•
Eliminate duplicative columns from the same table.
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