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First Normal Form

If a relation contains no repeating groups, then it is in first normal form. Conversely, if we find that for a single primary key, we have

two data items that we need to 'squeeze' into one column, then the data cannot be in first normal form. Let's say that we've decided to

slap together a database containing information about patients and the (medicinal) drugs they are taking. So we create a table with thefollowing columns, including the primary key "Patient ID Number":

Patient ID

Number

Patient

NameDrug Trade Name

Formulatio

nSize Dose Frequency Side Effect

Let's try filling in some information..

Patient ID

Number

Patient

NameDrug

Trade

Name

Formulatio

n

Size Dose Frequency Side Effect

6009315011076 Soap,JoeCarbimazole

Carbamazepine

Neomercazole

Tegretol

Tab

Caps

10mg

200mg

30mg

200mg

OD

TDS

Agranulocytosis

nil

6003325011074 Green,Anne CarbimazoleNeomercaz

oleTab 10mg 10mg OD nil

Woops. At the intersection of some rows and columns, we've had to fill in two different data items. It's also obvious that there is

considerable redundancy in the table - the drug Carbimazole (with all the associated information) is represented twice.

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Fixing to First Normal Form

It should be clear that we can fix things by simply introducing a "composite primary key" - we can group the drug and the patient ID

together as a composite primary key, so now each row has a unique primary key, and at no intersection of row and column do we have

to put in two data items:

Patient ID

NumberDrug

Patient

Name

Trade

NameFormulation Size Dose Frequency Side Effect

6009315011076 Carbimazole Soap, JoeNeomercazole

Tab 10mg 30mg OD Agranulocytosis

6009315011076 Carbamazepine Soap, Joe Tegretol Caps 200mg 200mg TDS nil

6003325011074 Carbimazole Green,AnneNeomerca

zoleTab 10mg 10mg OD nil

Equally clearly, this is a clumsy fix, and really hasn't changed much. We still have immense data redundancy. We need to go furtherto..

Second Normal Form

Note that, although the above table is now in 'first normal form', nothing much has changed. Look at the table carefully, and you'll see

that there are what we call partial dependencies. In other words, the columns Trade Name,Formulation, and Size depend only on theDrug component of the key, and not on the other part of the key, Patient ID Number. Likewise, thePatient Name depends only on

the Patient ID Number, and is not dependent at all on the Drug column! To get rid of this problem, we create two new tables, a

Patient Table:

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Patient

Patient ID Number Patient Name

6009315011076 Soap, Joe

6003325011074 Green,Anne

and a Drug Table:

Drug

Drug Trade Name Formulation Size

Carbimazole Neomercazole Tab10mg

Carbamazepine Tegretol Caps 200mg

Finally, we relate the two in a diminished form of our original table, thus:

PatientRx

Patient ID Number Drug Dose Frequency Side Effect

6009315011076 Carbimazole 30mg OD Agranulocytosis

6009315011076 Carbamazepine 200mg TDS nil

6003325011074 Carbimazole 10mg OD nil

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Third Normal Form

.. but still we're not finished. Look at the last table carefully. There's an intimate relationship between the the dose and the frequencyof giving a drug. Here's where knowledge of your subject comes in. Many people would be happy to stop at this point. There is no

absolutely fixedrule that says you have to give your carbamazepine at a dose of 200mg TDS - in fact, if you're religiously doing so,you're probably mistreating a lot of your epileptics. But let's say the whole point of our drug survey is to relate different drug regimensand associated side effect! In this context, we have a strong association between the dose and frequency of a drug. We call such a

relationship between two non-key attributes a transitive dependency.

Third normal form is about removing transitive dependencies. How could we do this? Well, we could label each dose + frequency as a

"regimen", and proceed to break up thePatientRx table into two, thus:

PatientRx

Patient ID Number Drug Regimen Side Effect

6009315011076 Carbimazole R1 Agranulocytosis

6009315011076 Carbamazepine R3 nil

6003325011074 Carbimazole R2 nil

with a newDrugRegimen table:

DrugRegimen

Regimen Dose Frequency

R1 30mg OD

R2 10mg OD

R3 200mg TDS