Database Design (Normalizations)

DCO11310

Database Systems and Design

By Rose Chang

Logical Data Model

1. Build a Conceptual Data Model2. Build and validate logical data model (LDM)

Drive relations for LDM Validate relations using normalisation Validate relations against user transactions Check integrity constraints Review LDM with user Merge LDMs into global model

Top-down Modeling

Entity - Entity - Entity

DATABASE

Table - Table – Table - Table - Table

Attributes+

Constraints

Attributes+

Constraints

Attributes+

Constraints

Attributes+

Constraints

Attributes+

Constraints

Bottom-up Modeling

Entity - Entity - Entity

DATABASE

Table - Table – Table - Table - Table

Attributes+

Constraints

Attributes+

Constraints

Attributes+

Constraints

Attributes+

Constraints

Attributes+

Constraints

Normalizations

A process that assigns attributes to entities in such a way that data redundancies are reduced or eliminated

Enables us to analyse the design of the database Identify the existence of potential data anomalies result from

those redundancies A step to step process : given a data model and the relevant

FDs Decomposition of relation schema based on knowledge of

underlying functional dependencies Results in a relational schema that satisfies certain important criteria:

1NF, 2NF, 3NF, BCNF, 4NF, … E.G., No anomalies, no spurious or invalid data during joins

Update Anomalies

Redundancies Information fact is stored in more than one place

Insertion anomalies Unable to insert a fact into table without having other facts (or

inserting nulls) Deletion anomalies

If a set of values becomes empty, we may lose other information as a side effect

Modification anomalies Change the information in one tuple but leave information

unchanged in another

Example

Real bad design: Study(Sid,name,Dept,Course_code, Course_name)

Sid Name Dept C_code C_Name

S01 Rose DCO 20401 DB

S01 Rose DCO 30198 Project

S02 Peter DCO 20401 DB

S03 Mary DCO 30198 Project

S04 Tom DCO 20401 DB

What are the Anomalies?

Redundancy Insertion Anomaly Deletion Anomaly What is the best design for this information?

No anomalies Can reconstruct all original information

Process of Normalization

Users User’s requirement

Forms/ Report

Other sourcesFrom company

Data sources

UNFTransfer attributes into table format

1NFRemove repeating group

2NF

Remove partial dependencies

3NFRemove transitive dependencies

Normalizations

Unnormalised Form (UNF) can be captured from data entities generated in System Analysis phase sample reports or screens

Invoice

Stf_name: Rose C W Chang Stf_ID. : 50121456Dept: Sales Dpt_Code: SAL

Item Code Item Description PriceI011 Wing-Type-A 70I012 Wing-Type-B 60I013 Engine-Type-A 70

Total 200

First Normal Form

A relation is in first normal form (1NF) if and only if All the key attributes are defined There are no repeating groups in the table All non-primary-key attribute is functionally

dependent on the primary key Problem : attributes not necessary fully

functionally dependent

Functional Dependencies

Attribute B is functionally dependent on attribute A if and only if each value of A is associated with precisely one value of B at any one time

E.G. Stf_name is functionally dependent on Stf_ID, Stf_ID Stf_name

The attribute on the left is a determinant

First Normal Form (1NF)

Eliminate repeating groups of data items

UNF 1NFStf_ID Stf_IDStf_name Stf_nameDept_code Dept_codeDept_name Dept_name{Item_code Item_desc Stf_ID Price } Item_code Item_desc

Price

Second Normal Form

A relation is in second normal form (2NF) if and only if It is in 1NF All non-primary-key attribute is fully

functionally dependent on the primary key, that is, there is no partial dependecy.

Full Functional Dependency

Attribute B is fully functionally dependent (FD) on attribute A if it is functionally dependent on A and NOT functionally dependent on any subset of A

All determinants in each relation are candidate keys

1NF 2NFStf_ID Stf_IDStf_name Stf_nameDept_code Dept_codeDept_name Dept_name

Stf_ID Stf_ID Item_codeItem_code Item_code Item_descItem_desc Price Price

Second Normal Form (2NF)

Record is in 1NF and no partly dependencies

Third Normal Form

A relation is in third normal form (3NF) if and only if It is in 2NF It contains NO transitive dependencies

transitive dependencies A condition where A, B, and C are attributes of a relation

such that if AB and BC, then C is transitively dependent on A via B (provided that A is not FD on B or C)

Third Normal Form (3NF)

Record is in 2NF and no transitive dependencies (no fields dependent on nonkey field(s))

2NF 3NFStf_ID Stf_ID Dept_codeStf_name Stf_name Dept_nameDept_code Dept_codeDept_name

Stf_ID Item_codeStf_ID Item_code Item_code Item_descItem_code Item_desc PricePrice

E/R Model after Normalization

Staff Sold Items

ItemDept

Normalize it to 3NF

Wellmeadows Hospital

Drug

Ward 11

Units per

Robert MacDonald

Orthopaedic

Name

10223 Morphine Pain Killer

Ward Number :

Ward Name :

Full Name :

P10034 Patient Number :

Patient Medication Form

84 Bed Number :

Dosage Description

10mg/ml 50

Number Day

Start

24/03/96

Date

Finish

24/04/96

Date

10334 Tetracyclene Antibiotic 0.5mg/ml 10 24/03/96 17/04/96

10223 Morphine Pain Killer 10mg/ml 10 25/04/96 02/05/96

Method

Admin

Oral

IV

Oral

of

Q & A

Readings:Connolly: Ch13, except BCNF, 4NF & 5NF