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LabExperiment2Report

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Introduction

Lab Experiment 2: Database Table creation,

Maintenance & Views

2.3: Preparation

(1)

The primary key of a table is a column (or combination of columns in a table) that are used to uniquely identify rows in a table. This means that two different rows in a table may never have the same value in their primary key, and for every row in the table the primary key must have a value.

Therefore, if the primary key column(s) are declared NULL, two or more rows in the primary key can have identical values and thus they will NOT be unique. Also the definition of the primary key states that a primary key must

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Middle

basically states that the entity is in the 1NF if it consists of a Primary Key.

By analysing the two tables, SUPPLIER and INVENTORY, it is evident that they both consist of a primary key attribute.

In the SUPPLIER table the primary key attribute is the CODE attribute, where as in the INVENTORY table it is the ITEM_CODE attribute.

 A table is in the 2nd Normalisation Form (2NF) if it is in the 1NF and no attribute is dependent on only a portion of the primary key.

The SUPPLIER table has a single attribute primary key. Thus by default, this table is in the 2NF.

On the other hand, the INVENTORY

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Conclusion

SUPPLIER (CODE, NAME, CONTACT, ADDRESS 1, ADDRESS 2, PHONE, FAX).

The SUPPLIER table is now in 3NF, as it does not consist of any transitive dependencies.

The new table is called SUPPLIER_ADDRESS and it contains attributes that were involved in the transitive dependency in SUPPLIER table.

SUPPLIER_ADDRESS(SUPPLIER, POST_CODE, TOWN)

The new table is normalised because it complies with the rules of the 1NF, 2NF and 3NF.

The INVENTORY table is free of any transitive dependencies, so it is in the 3NF.

(5)

The many-to-many (m:m) relationship between the STUDENT entity and the MODULE entity is broken down into two, one-to-many (1:m) relationships, with a creation of a new entity called STUDENT_MODULE.

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